Category: Reputation, filtering and blacklists

This guide explains how to monitor your sending domain and IP against email blacklists and how to respond if a listing is detected as a Sender user.

Why this matters

If your domain or sending IP appears on a blacklist, mailbox providers may reject your emails outright or route them to spam. Blacklisting is one of the most severe reputation events a sender can experience, and it directly reduces inbox placement across all recipient providers. Proactive monitoring allows you to detect a listing early, identify the cause, and begin the delisting process before sustained delivery failures damage your sender reputation further.

How to identify the problem

Hard bounce rate on the Dashboard — Go to Dashboard and review the Hard bounce rate metric in the Traffic and reach report section. A sudden spike in hard bounces, particularly from a single mailbox provider, often indicates that your IP or domain has been blacklisted by that provider or by a blacklist it references.

Average spam rate on the Dashboard — Check the Average spam rate metric on the Dashboard. A rising spam rate signals that recipients are marking your emails as spam, which contributes to blacklist listings. An Average spam rate above 0.1% is a warning sign that blacklisting may follow.

Total spams on the Dashboard — Review the Total spams count in the Traffic and reach report on the Dashboard. A high absolute number of spam reports over a short period increases the likelihood that blacklist operators will flag your sending infrastructure.

MXToolbox Blacklist Check — Use MXToolbox (mxtoolbox.com/blacklists.aspx) to run a multi-blacklist lookup against your sending domain or IP address. This tool checks your domain and IP against dozens of blacklists simultaneously and reports any active listings.

Spamhaus Lookup — Search your domain and sending IP on Spamhaus (check.spamhaus.org). Spamhaus operates several widely used blacklists including the SBL (Spamhaus Block List) and DBL (Domain Block List). A listing on Spamhaus has a high impact because many mailbox providers reference it directly.

Google Postmaster Tools — If you send to Gmail recipients, check Google Postmaster Tools (postmaster.google.com) for domain reputation data. A reputation rating of "Bad" or "Low" alongside delivery failures to Gmail may indicate an active blacklisting or severe reputation degradation.

Steps to monitor and respond

Step 1 — Run a blacklist check on your domain and IP

Open MXToolbox (mxtoolbox.com/blacklists.aspx) and enter your sending domain. Run the lookup to scan across multiple blacklists at once. Note any blacklists where your domain or IP is listed. Then repeat the check on Spamhaus (check.spamhaus.org) specifically, since Spamhaus listings have the widest impact on delivery. Record which blacklists show an active listing and the reason provided.

Step 2 — Correlate with Sender dashboard metrics

Go to your Dashboard in Sender and review the Hard bounce rate, Average spam rate, and Total spams in the Traffic and reach report. Compare the date when these metrics spiked against the approximate listing date shown by the blacklist provider. This helps you identify the sending behavior or campaign that triggered the listing, whether it was a high-complaint campaign, a list with outdated addresses, or a spam trap hit.

Step 3 — Submit a delisting request

Visit the blacklist provider's website and follow their delisting process. For Spamhaus, submit a removal request through their lookup tool after addressing the underlying cause. For Barracuda, use the Barracuda Central removal request form. For SORBS, follow the delisting instructions on their lookup page. Each provider requires that you describe the corrective action you have taken. Do not request delisting until you have identified and resolved the root cause.

Step 4 — Address the root cause

Based on the metrics from Step 2, take corrective action. If Average spam rate is elevated, review recent campaign content and subscriber sources. If Hard bounce rate spiked, clean your subscriber list by removing invalid addresses — go to Subscribers and filter by bounce status. If you suspect a spam trap hit, remove subscribers who have not engaged (opened or clicked) in the past 6–12 months. These actions prevent re-listing after delisting.

Step 5 — Monitor continuously after delisting

After your delisting request is approved, schedule regular blacklist checks using MXToolbox at least weekly for the first month. Continue reviewing Hard bounce rate, Average spam rate, and Total spams on the Dashboard after each campaign send. If metrics remain stable and no new listings appear, extend your monitoring cadence to biweekly or monthly. Re-listing can occur quickly if the underlying issue was not fully resolved.

How filtering works

Blacklist-based filtering — Mailbox providers query blacklists such as Spamhaus, Barracuda, and SORBS during the SMTP connection or message evaluation. If the sending IP or domain is listed, the provider may reject the message at the connection level or route it directly to spam. Different providers reference different blacklists, so a single listing may affect delivery to some providers but not others.

IP reputation scoring — Mailbox providers maintain internal reputation scores for sending IP addresses based on bounce rates, spam complaints, spam trap hits, and sending volume patterns. A blacklist listing typically occurs after the IP reputation has already degraded past a threshold. Recovering the IP reputation requires sustained clean sending behavior even after a blacklist removal.

Domain reputation scoring — In addition to IP reputation, providers like Gmail evaluate the reputation of your sending domain independently. Domain-based blacklists such as the Spamhaus DBL and SURBL list domains found in spam messages. A domain listing can affect delivery regardless of which IP you send from, making domain reputation monitoring equally important.

Spam trap detection — Blacklist operators maintain spam trap email addresses — addresses that should never receive email because they were either abandoned or were never associated with a real user. Sending to a spam trap signals poor list acquisition or maintenance practices. A single spam trap hit on a high-priority blacklist like Spamhaus can result in an immediate listing.

Feedback loop data — Some mailbox providers operate feedback loops (FBLs) that report back to senders when a recipient marks an email as spam. High complaint volumes reported through FBLs contribute to blacklist listings over time. Monitoring your Total spams and Average spam rate on the Sender Dashboard reflects this complaint data.

Recovery tips

Fix the root cause before requesting delisting — Blacklist providers review delisting requests and may deny them or re-list your IP/domain if the underlying issue persists. Identify whether the cause was a bad list segment, spam trap exposure, or a content issue before submitting a request.

Reduce sending volume temporarily — After a blacklist event, lower your sending volume and send only to your most engaged subscribers. This generates positive engagement signals and helps rebuild IP and domain reputation with mailbox providers.

Remove unengaged subscribers — Go to Subscribers in Sender and identify contacts who have not opened or clicked in the past 6–12 months. Removing these subscribers reduces the risk of hitting spam traps and improves overall engagement rates, which supports reputation recovery.

Send a re-engagement campaign first — Before resuming full-volume sending, send a targeted re-engagement campaign to moderately active subscribers. Monitor the resulting Hard bounce rate and Average spam rate on the Dashboard closely. If metrics remain clean, gradually increase volume.

Set up ongoing monitoring — Use MXToolbox to schedule automated blacklist monitoring alerts for your domain and IP. Combine this with regular reviews of your Dashboard metrics in Sender. Early detection of a re-listing allows faster corrective action.

Common issues

Listed on a blacklist but emails are still delivering → Not all mailbox providers reference the same blacklists. A listing on a smaller or less-referenced blacklist may not immediately affect delivery. However, you should still request delisting promptly, as blacklist data can propagate to other providers over time.

Delisting request was denied → The blacklist provider determined that the root cause has not been addressed. Review the denial reason, take the required corrective action (such as cleaning your list or reducing complaints), and resubmit the request. Some providers enforce a waiting period before you can resubmit.

Re-listed shortly after successful delisting → This indicates the underlying problem was not fully resolved. Common causes include continued sending to spam traps, ongoing high complaint rates, or a compromised subscriber list. Review your Hard bounce rate and Average spam rate on the Dashboard, clean your list more aggressively, and reduce volume before requesting delisting again.

Blacklist check shows a listing on an IP you don't recognize → If you are on a shared IP plan, another sender's behavior may have caused the listing. Contact Sender support to confirm your sending IP allocation and discuss whether a dedicated IP is available for your account.

Dashboard metrics look normal but delivery is declining → Some blacklist listings affect only specific providers. Check Google Postmaster Tools for Gmail-specific reputation data, and use MXToolbox to verify your status across multiple blacklists. A domain-level listing on Spamhaus DBL or SURBL may not surface in standard IP blacklist checks.

FAQs

How do I know if my domain is on a blacklist?

Use external tools like MXToolbox, Spamhaus Lookup, or Barracuda Reputation to check your domain and sending IP. If listed, follow the blacklist provider's delisting process. Monitor your Hard bounce rate and Average spam rate on the Sender Dashboard for signs of blacklisting, such as a sudden spike in rejections from a specific provider.

How long does it take to recover sender reputation after a blacklisting?

Recovery time varies depending on the severity of the listing and the actions taken. Minor listings on smaller blacklists may resolve within days of delisting. Severe reputation damage from a Spamhaus listing combined with high complaint rates can take several weeks to months of clean sending to recover from. Consistent, low-volume sending to engaged subscribers accelerates recovery.

What is a spam trap and how does it affect my reputation?

A spam trap is an email address used by blacklist operators or mailbox providers to identify senders with poor list practices. Sending to a spam trap signals that your list contains unverified or outdated addresses. This can result in blacklisting or reduced inbox placement. Remove inactive subscribers regularly to reduce spam trap risk.

Does Sender share my sending IP with other users?

Sender's infrastructure and IP allocation policies may vary by plan. Check your account settings or contact Sender support to understand whether your account uses shared or dedicated IPs, as this affects how other senders' behavior may influence your reputation.

Why are my emails going to spam even though I'm not on any blacklist?

Blacklist status is only one factor in filtering decisions. Mailbox providers also evaluate sender reputation scores, engagement rates, complaint rates, and content quality independently. If your blacklist checks are clean but emails land in spam, review your Average spam rate and engagement metrics on the Dashboard, and check Google Postmaster Tools for domain reputation data specific to Gmail.

This guide explains what sender reputation is, how mailbox providers evaluate it, and how to monitor and protect it as a Sender user.

Why this matters

Sender reputation is a score that mailbox providers (Gmail, Outlook, Yahoo) assign to your sending domain and IP address based on your email sending behavior. A strong reputation means your emails reach the inbox; a damaged reputation causes emails to land in spam or get rejected entirely. Every campaign you send contributes to this score, making ongoing monitoring essential to maintaining consistent inbox placement.

How to identify the problem

Hard bounce rate — Open your Dashboard and check the Hard bounce rate in the Traffic and reach report section. A hard bounce rate above 2% signals that your list contains invalid addresses, which degrades your reputation with mailbox providers.

Average spam rate — On the Dashboard, review the Average spam rate metric below the chart. A spam rate above 0.1% is a warning sign. Rates above 0.3% can cause mailbox providers to throttle or filter your emails aggressively.

Campaign-level spam reports — Navigate to Email campaigns, select a sent campaign, and open the Campaign overview. In the Statistics section, check the spam reports count. A spike in spam reports on a specific campaign indicates content or targeting issues that need immediate attention.

Google Postmaster Tools — If you send to Gmail recipients, check Google Postmaster Tools for your domain's reputation rating (High, Medium, Low, Bad). This external tool provides domain-level reputation data that supplements Sender's built-in metrics and shows how Gmail specifically views your sending behavior.

MXToolbox Blacklist Check — Run your sending domain and IP through MXToolbox Blacklist Lookup to check whether you appear on any major blacklists. Being listed on blacklists such as Spamhaus, Barracuda, or SORBS directly causes email rejections and filtering.

Steps to monitor and protect your reputation

Step 1 — Review your Dashboard metrics weekly

Go to Dashboard and review the Traffic and reach report. Check the Hard bounce rate, Average spam rate, and Bounce rate values. Compare them over time using the date selector in the top right corner. If any metric trends upward across multiple sending periods, investigate the cause before sending your next campaign. Healthy sending shows a hard bounce rate below 2% and a spam rate below 0.1%.

Step 2 — Audit campaign-level performance after each send

After each campaign, navigate to Email campaigns, open the sent campaign, and review the Statistics section on the Campaign overview page. Compare spam reports, hard bounced, soft bounced, and unsubscribed counts against previous campaigns. If spam reports or hard bounced numbers are higher than usual, pause sending and review your recipient list and content before the next campaign.

Step 3 — Check external reputation tools monthly

Visit Google Postmaster Tools to review your domain reputation and spam rate as reported by Gmail. Run a blacklist check on MXToolbox for both your sending domain and IP. If your domain reputation is rated Low or Bad in Google Postmaster Tools, or if you appear on any blacklist, take corrective action immediately — reduce sending volume and focus only on your most engaged subscribers.

Step 4 — Clean your subscriber list regularly

Go to Subscribers and use the Email status filter to identify inactive or problematic addresses. Remove subscribers who have not opened or clicked any email in the last 90–120 days. Sending to disengaged recipients lowers your engagement rate, which mailbox providers interpret as a negative reputation signal. Regular list hygiene also reduces the risk of hitting spam traps.

Step 5 — Monitor transactional email metrics separately

Navigate to Transactional emails → Metrics and check the Hard bounces and Spam reports counts. Transactional emails contribute to your domain reputation just like marketing campaigns. Filter by Domain to isolate performance per sending domain. If transactional emails show rising bounces or spam reports, verify that your transactional sending triggers and recipient data are accurate.

How filtering works

Reputation scoring — Mailbox providers assign a reputation score to your sending domain and IP address based on historical sending patterns. This score incorporates bounce rates, spam complaint rates, engagement metrics, and blacklist status. A low score causes your emails to be filtered to spam or rejected outright.

Engagement-based filtering — Providers like Gmail weigh recipient engagement heavily. If recipients consistently open, click, and reply to your emails, your reputation strengthens. If recipients ignore, delete, or mark your emails as spam, your reputation degrades. This is why sending to engaged subscribers is critical for inbox placement.

Content filtering — Spam filters analyze email content for patterns associated with spam, including excessive use of capital letters, misleading subject lines, heavy image-to-text ratios, and known spam phrases. Content filtering works alongside reputation scoring — poor content can trigger spam placement even when reputation is otherwise healthy.

Blacklist filtering — Blacklist operators like Spamhaus, Barracuda, and SORBS maintain lists of IPs and domains associated with spam. Mailbox providers query these blacklists in real time. If your domain or IP appears on a blacklist, providers may reject your emails entirely or route them to spam regardless of other reputation signals.

Feedback loops — Mailbox providers send complaint data back to email service providers like Sender when a recipient marks an email as spam. Sender processes this data and reflects it in your spam reports metric. High complaint rates through feedback loops directly lower your reputation score with the reporting provider.

Recovery tips

Reduce sending volume — If your reputation is damaged, temporarily reduce your sending volume and frequency. Send only to your most engaged subscribers to generate positive engagement signals and gradually rebuild trust with mailbox providers.

Remove problematic addresses — Go to Subscribers and remove addresses that have hard bounced, repeatedly soft bounced, or generated spam complaints. Continuing to send to these addresses accelerates reputation damage.

Send re-engagement campaigns — Before removing inactive subscribers entirely, send a targeted re-engagement campaign to a small segment. Subscribers who do not engage after re-engagement should be removed from your active list to prevent further reputation harm.

Request delisting if blacklisted — If you find your domain or IP on a blacklist through MXToolbox, visit the blacklist provider's website (such as Spamhaus, Barracuda, or SORBS) and submit a delisting request. Most providers require you to demonstrate that the underlying issue has been resolved before granting removal.

Monitor continuously after correction — After taking corrective action, monitor your Dashboard metrics and Google Postmaster Tools daily for at least two weeks. Reputation recovery is gradual, and sustained improvement in bounce rates, spam rates, and engagement is necessary to restore inbox placement.

Common issues

Sudden spike in hard bounces → This typically happens after importing an old or unverified list. Remove all hard-bounced addresses immediately from Subscribers and avoid importing lists that have not been verified recently.

Emails going to spam despite low complaint rates → Low engagement (opens and clicks) can cause spam placement even without complaints. Review your Campaign overview → Statistics for opened and unique clicks rates, and segment your list to target only active subscribers.

Blacklisted after a single campaign → Sending a large volume to an unclean list can trigger blacklisting in one send. Check MXToolbox for listings, submit delisting requests, and reduce your next send volume significantly while focusing on list quality.

Reputation differs across providers → Gmail, Outlook, and Yahoo use independent reputation systems. Your emails may reach the inbox at one provider but land in spam at another. Use Google Postmaster Tools for Gmail-specific data, and review per-provider patterns in the Performance by inbox provider report on the Campaign overview page (available on Pro plans).

Spam rate rising gradually over time → This signals list fatigue or a growing number of disengaged recipients. Check the Average spam rate on your Dashboard over progressively longer date ranges. Implement regular list cleaning and re-engagement workflows to reverse the trend.

FAQs

How do I know if my domain is on a blacklist?

Use external tools like MXToolbox, Spamhaus Lookup, or Barracuda Reputation to check your domain and sending IP. If listed, follow the blacklist provider's delisting process. Monitor your Hard bounce rate and Average spam rate on the Dashboard for signs of blacklisting, such as a sudden spike in rejections from a specific provider.

How long does it take to recover sender reputation?

Recovery time varies depending on the severity of the damage and the actions taken. Minor issues may resolve within one to two weeks of corrected sending behavior. Severe reputation damage, such as sustained high spam complaint rates, can take several weeks to months. Consistent, lower-volume sending to engaged subscribers accelerates recovery.

What is a spam trap and how does it affect my reputation?

A spam trap is an email address used by blacklist operators or mailbox providers to identify senders with poor list practices. Sending to a spam trap signals that your list contains unverified or outdated addresses. This can result in blacklisting or reduced inbox placement. Remove inactive subscribers regularly through the Subscribers section to reduce spam trap risk.

Does Sender share my sending IP with other users?

Sender's infrastructure and IP allocation policies may vary by plan. Check your account settings or contact Sender support to understand whether your account uses shared or dedicated IPs, as this affects how other senders' behavior may influence your reputation.

Why are my emails going to spam even though authentication passes?

Authentication (SPF, DKIM, DMARC) is necessary but not sufficient for inbox placement. Mailbox providers also evaluate sender reputation, engagement rates, complaint rates, and content quality. If your emails pass authentication but land in spam, focus on improving engagement metrics visible in your Campaign overview → Statistics, reducing complaints, and reviewing your content for spam trigger patterns.

This guide explains how spam filters evaluate your emails and what practices help you avoid filtering, so your campaigns reach the inbox consistently.

Why This Matters

Spam filters are the primary gatekeepers between your sent email and the recipient's inbox. Even with valid authentication, mailbox providers like Gmail, Outlook, and Yahoo evaluate multiple signals — including sender reputation, engagement history, complaint rates, and content patterns — before deciding whether to deliver your email to the inbox or route it to spam. Failing any of these checks reduces your inbox placement and can trigger long-term reputation damage that takes significant effort to reverse.

How to Identify the Problem

Average spam rate on the Dashboard — Go to Dashboard and review the Average spam rate in the Traffic and reach report section. Any value above 0.1% signals that a meaningful share of recipients are marking your emails as spam, which directly impacts how mailbox providers filter your future sends.

Hard bounce rate on the Dashboard — In the same Traffic and reach report, check the Hard bounce rate. A rate above 2% suggests your list contains invalid addresses, which spam filters interpret as a sign of poor list hygiene and increases your likelihood of being filtered.

Spam reports per campaign — Open any sent campaign from Email campaigns, then review the Statistics section on the Campaign overview page. The spam reports metric shows how many recipients in that specific send flagged your email as spam. A spike in this value for a single campaign may indicate a content or targeting issue.

Performance by inbox provider — On the Campaign overview page, select Performance by inbox provider in the left sidebar (available on PRO plans). The Statistics by provider table displays Spam report rate and Bounce rate broken down by inbox provider, which helps you identify whether a specific provider is filtering your emails more aggressively than others.

External blacklist tools — Use MXToolbox, Spamhaus Lookup, or Barracuda Reputation to check whether your sending domain or IP has been blacklisted. A blacklisting causes widespread filtering or outright rejection of your emails across multiple providers.

Steps to Reduce Spam Filtering

Step 1 — Review your spam and bounce metrics

Go to Dashboard and check the Average spam rate and Hard bounce rate in the Traffic and reach report. Keep your spam rate below 0.1% and hard bounce rate below 2%. If either metric exceeds these thresholds, your emails are at increased risk of being filtered. Next, open your most recent sent campaigns in Email campaigns and review the spam reports and hard bounced values in the Statistics section on each Campaign overview page to identify which specific sends are contributing to the problem.

Step 2 — Clean your list and target engaged subscribers

Go to Subscribers and use the Email status filter to identify subscribers with a Bounced or Reported spam status. Remove or suppress these contacts to prevent further damage to your reputation. Then go to Subscribers → Segments and review the Unengaged subscribers 180 days segment. Exclude unengaged subscribers from your campaigns. Sending to recipients who do not open or click your emails lowers your engagement rates, which mailbox providers interpret as a negative signal when making filtering decisions.

Step 3 — Audit your email content for spam triggers

Before sending, review your email content for patterns that spam filters flag. Avoid using excessive capitalization, misleading subject lines, image-only layouts without text, and URL shorteners. Ensure your email includes a visible unsubscribe link and that your "From" name and address are recognizable to recipients. Use a consistent sending domain and avoid switching sender identities between campaigns. After sending, check the spam reports value on the Campaign overview page to confirm your content adjustments reduced complaint rates.

Step 4 — Send to the right audience at the right frequency

Use the pre-built segments under Subscribers → Segments — specifically Highly engaged subscribers and Engaged subscribers 180 days — to target recipients who interact with your emails. Sending to engaged recipients produces higher open and click rates, which strengthens your reputation with mailbox providers. Avoid sending too frequently, as this increases unsubscribes and complaints. Monitor the Unsubscribe rate and Average spam rate on the Dashboard after adjusting your send frequency to verify improvement.

Step 5 — Monitor inbox provider performance over time

After each campaign, go to the Campaign overview page and select Performance by inbox provider. Review the Open rate, Bounce rate, and Spam report rate columns in the Statistics by provider table. If a specific provider shows significantly lower open rates or higher spam report rates than others, your emails are likely being filtered by that provider. Use external tools like Google Postmaster Tools (for Gmail) to get additional domain-level reputation data that supplements the metrics available in Sender.

How Filtering Works

Sender reputation scoring — Mailbox providers assign a reputation score to your sending domain and IP based on historical sending behavior. This score incorporates bounce rates, spam complaint rates, engagement rates, and sending volume consistency. A low reputation score causes providers to route your emails to spam or reject them outright, regardless of content quality.

Content analysis — Spam filters scan your email content for patterns associated with spam, including excessive use of capital letters, certain trigger phrases, misleading subject lines, a high image-to-text ratio, and embedded URL shorteners. Filters also check whether your content matches patterns seen in previously reported spam. Even emails from reputable senders can be filtered if the content triggers enough negative signals.

Engagement-based filtering — Providers like Gmail and Yahoo track how recipients interact with your emails over time. High open rates, clicks, and replies signal that your emails are wanted, which improves future inbox placement. Low engagement — especially when combined with deletions without opening — tells the provider that recipients do not value your emails, increasing the likelihood of spam folder placement for future sends.

Complaint feedback loops — When a recipient clicks "Report spam" or "Mark as junk," that complaint is sent back to the email service provider through a feedback loop. Sender processes these complaints and marks the subscriber's status as Reported spam in the Subscribers list. A high complaint rate directly damages your sender reputation and increases filtering across all providers.

Blacklist-based filtering — Blacklist operators like Spamhaus, Barracuda, and SORBS maintain lists of IPs and domains associated with spam. Mailbox providers query these blacklists during the delivery process. If your sending IP or domain appears on a blacklist, your emails may be rejected or filtered by any provider that checks that list.

Recovery Tips

Reduce sending volume temporarily — If your Average spam rate or Hard bounce rate has spiked, reduce your sending volume and send only to your most engaged subscribers. Use the Highly engaged subscribers segment under Subscribers → Segments to limit your audience while you rebuild reputation.

Remove all problematic contacts — Filter your Subscribers list by the Bounced and Reported spam statuses using the Email status filter. Remove these contacts from your active lists to stop sending to addresses that generate negative signals.

Check for blacklisting and request delisting — Use MXToolbox or Spamhaus Lookup to check your domain and sending IP. If listed, submit a delisting request through the blacklist provider's website and address the underlying cause (such as list hygiene or high complaint rates) before requesting removal.

Re-engage gradually — After cleaning your list and reducing complaints, slowly increase your sending volume over several weeks. Start with your most engaged segments and gradually expand to broader audiences as your metrics stabilize.

Monitor continuously after changes — After each send, check the Average spam rate, Hard bounce rate, and spam reports metrics on the Dashboard and Campaign overview pages. Consistent improvement across multiple sends confirms that your corrective actions are working.

Common Issues

Emails go to spam despite passing authentication → Authentication (SPF, DKIM, DMARC) is necessary but not sufficient. Mailbox providers also evaluate reputation, engagement, complaints, and content. Review your Average spam rate and engagement metrics on the Dashboard, and audit your content for spam trigger patterns.

Spam rate suddenly increases after a campaign → This typically happens when you send to an unclean list, a purchased list, or a segment with many inactive subscribers. Check the spam reports metric on the Campaign overview page for that campaign, then filter your Subscribers list by Reported spam status to identify and remove the affected contacts.

Low open rates at a specific inbox provider → Go to Performance by inbox provider on the Campaign overview page and compare Open rate and Spam report rate across providers. If one provider shows significantly worse metrics, your reputation with that provider may be damaged. Use Google Postmaster Tools for Gmail-specific reputation data.

Bounce rate spikes without changes to list → This can indicate that your sending IP or domain has been blacklisted. Check MXToolbox or Spamhaus Lookup for listings. Also review the Hard bounce rate and Soft bounce rate on the Dashboard to determine whether the bounces are permanent (invalid addresses) or temporary (server-side filtering).

Unengaged subscribers drag down performance → Subscribers who never open your emails reduce your overall engagement rate, which mailbox providers use as a filtering signal. Go to Subscribers → Segments and review the Unengaged subscribers 180 days segment. Exclude or remove these contacts from future campaigns.

FAQs

How do I know if my domain is on a blacklist? Use external tools like MXToolbox, Spamhaus Lookup, or Barracuda Reputation to check your domain and sending IP. If listed, follow the blacklist provider's delisting process. Monitor your Hard bounce rate and spam reports in Sender for signs of blacklisting, such as a sudden spike in rejections from a specific provider.

How long does it take to recover sender reputation? Recovery time varies depending on the severity of the damage and the actions taken. Minor issues may resolve within 1–2 weeks of corrected sending behavior. Severe reputation damage, such as sustained high spam complaint rates, can take several weeks to months. Consistent, low-volume sending to engaged subscribers accelerates recovery.

What is a spam trap and how does it affect my reputation? A spam trap is an email address used by blacklist operators or mailbox providers to identify senders with poor list practices. Sending to a spam trap signals that your list contains unverified or outdated addresses. This can result in blacklisting or reduced inbox placement. Remove inactive subscribers regularly using the Unengaged subscribers 180 days segment to reduce spam trap risk.

Does Sender share my sending IP with other users? Sender's infrastructure and IP allocation policies may vary by plan. Check your account settings or contact Sender support to understand whether your account uses shared or dedicated IPs, as this affects how other senders' behavior may influence your reputation.

Why are my emails going to spam even though authentication passes? Authentication (SPF, DKIM, DMARC) is necessary but not sufficient for inbox placement. Mailbox providers also evaluate sender reputation, engagement rates, complaint rates, and content quality. If your emails pass authentication but land in spam, focus on improving engagement, reducing complaints, and reviewing your content for spam trigger patterns. Check the Average spam rate and Performance by inbox provider data in Sender for diagnostic clues.