Why would deliverability drop if my bounce rate is still low?

This often means your emails are being filtered directly to the spam folder , or even discarded by mailbox providers. These actions do not always generate a bounce notification, making it appear as though your bounce rate is low. It's a strong indicator of a diminished sender reputation at the ISP level, which can be affected by factors like low engagement, hitting spam traps, or being listed on a private blocklist.

My spam rate is low. Why am I still facing deliverability issues?

While your direct spam complaint rate might be low, mailbox providers also consider indirect signals of dissatisfaction. This includes low open rates, recipients moving emails to spam manually (even if they don't click the report spam button), or even hitting spam traps set up by ISPs. These silent complaints or issues can severely impact your sender reputation and deliverability without a visible spike in your reported spam rate.

Could small changes to my email content or sending pattern cause a sudden drop?

Absolutely. Unexpected changes in your email content, a sudden increase or decrease in sending volume, or even a shift in your audience's engagement over time can trigger deliverability issues. Identifying the exact cause requires a thorough audit of your email program, including your list quality, sending patterns, and authentication records.

What are the immediate steps I should take?

Start by checking your blocklist status and reviewing your sender reputation using tools like Google Postmaster Tools. Implement a strict list hygiene regimen to remove inactive or risky addresses. Ensure all your email authentication (SPF, DKIM, DMARC) records are valid. Finally, focus on improving engagement through personalized and valuable content, and consider segmenting or suppressing unengaged subscribers. These are key steps to resolve deliverability issues .

Why has my email deliverability dropped significantly, despite a low spam rate and bounce rate, and what steps can I take to resolve it? - Troubleshooting - Email deliverability - Knowledge base

Experiencing a sudden and significant drop in email deliverability can be incredibly frustrating, especially when your spam rate and bounce rate metrics seem to be in good standing. Many marketers scratch their heads, wondering how a healthy list and clean sending practices could lead to emails not reaching the inbox.

The truth is, while low spam complaints and bounce rates are positive indicators, they don't tell the entire story of your sender reputation and how mailbox providers view your email program. A delivery rate plummeting from 99.6% to 80%, for instance, suggests that 20% of your emails are simply disappearing into a void, not necessarily bouncing back.

This scenario often points to deeper issues beyond the obvious metrics, such as silent filtering to spam folders, ISP-level blocklisting, or engagement problems that aren't immediately apparent. It means your messages are being accepted by the receiving server but then routed away from the primary inbox, or even dropped entirely without a bounce notification.

Hidden reputation triggers

When your deliverability drops without an increase in bounces, it often indicates that emails are being accepted by recipient servers but then diverted to the spam or junk folder, or simply discarded. This is where sender reputation becomes paramount. Internet Service Providers (ISPs) like

Google and

Yahoo analyze numerous factors beyond just bounces and spam complaints to assess your trustworthiness. These factors contribute to your domain reputation and IP reputation.

A key reason your emails might be silently blocked or filtered is due to a listing on a major email blacklist (or blocklist). Even with a low apparent spam rate, if you land on a significant blocklist, your emails could be rejected outright or heavily filtered. Organizations like Spamhaus are widely used by mailbox providers, and a listing there can instantly tank your deliverability.

It's also possible that your emails are being deferred rather than immediately bounced. Some systems might initially show messages as delivered but then bounce back later if a permanent delivery failure occurs after multiple retries. This can create a lag in reporting, making it seem like your bounce rate is low initially when, in fact, it might increase over time as deferred messages eventually fail.

Engagement and list quality issues

A low open rate, even if not explicitly shown as a high spam complaint, is a critical signal to mailbox providers. If recipients aren't opening or engaging with your emails, ISPs interpret this as disinterest or irrelevance, which negatively impacts your sender reputation and can lead to emails landing in the spam folder instead of the inbox. This is a common reason why open rates might drop.

Another subtle but impactful issue is spam traps. These are email addresses designed to catch senders who are not following best practices, like sending to old or purchased lists. Even a single hit on a spam trap can severely damage your sender reputation, leading to immediate blocklisting or heavy filtering without any bounce notifications. This explains why your bounce rate remains low despite a deliverability drop.

HubSpot community discussions often highlight how critical it is to manage unengaged contacts to avoid deliverability issues.

If you're using an older or less actively maintained email list, it might contain addresses that have become spam traps or simply inactive. While they might not hard bounce, sending to these addresses signals poor list hygiene to ISPs. Regular list cleaning and validation are crucial to prevent these silent deliverability killers.

Poor quality content or sudden changes in sending patterns can also trigger filters. If your email content suddenly becomes more promotional, includes suspicious links, or uses excessive spammy keywords, it could be flagged. Additionally, drastic increases or decreases in sending volume can raise red flags with mailbox providers, as consistency is a key factor in building trust. Reviewing your content for spam triggers is a good practice, as highlighted by

Brevo's best practices.

Technical compliance and infrastructure

Technical configurations like SPF, DKIM, and DMARC are fundamental to email authentication and reputation. Misconfigurations or recent changes to these records can lead to delivery issues. ISPs increasingly demand proper authentication, and failing these checks can result in emails being blocked or marked as spam without generating bounces.

For example, recent changes by

Microsoft and Google have put a stronger emphasis on email authentication for bulk senders. If your email setup is not fully compliant with their sender guidelines, your emails may face severe deliverability challenges. Checking your DMARC, SPF, and DKIM records is a crucial step.

Your sending infrastructure also plays a role. If you've recently changed Email Service Providers (ESPs) or integrated new sending platforms, there might be IP warming issues or configuration discrepancies causing the drop. Each sending IP has its own reputation, and sending large volumes from a new or cold IP can lead to throttling or blocking by mailbox providers.

Steps to resolve the issue

Resolving a sudden deliverability drop requires a systematic approach. Here's a table outlining key actions you can take:

Area	Action to take
Check Reputation	Monitor major blocklists like Spamhaus. Use Google Postmaster Tools and Outlook SNDS for insights into your sender reputation.
List Hygiene	Implement regular list cleaning to remove inactive or problematic addresses. Consider using a list verification service.
Authentication	Ensure your SPF, DKIM, and DMARC records are correctly set up and aligned. Use a DMARC record generator if needed.
Content Review	Check your email content for potential spam triggers, including suspicious links or overly promotional language.
Engagement	Re-engage inactive subscribers or segment them out. Make it easy for subscribers to manage their preferences or unsubscribe clearly.

Beyond these, I'd strongly recommend regularly using an email deliverability tester to diagnose potential issues before they escalate. This can help you understand how different mailbox providers are scoring your emails.

Remember, improving your email deliverability is an ongoing process. Consistent monitoring, proactive list hygiene, and adherence to email best practices are key to maintaining a strong sender reputation and ensuring your emails consistently reach the inbox.

Views from the trenches

Best practices

Maintain consistent sending volumes to avoid sudden spikes or drops that can trigger ISP filters.

Segment your audience and personalize content to increase engagement and reduce unsubscription rates.

Regularly monitor your domain and IP reputation using tools like Postmaster Tools.

Ensure all email authentication protocols (SPF, DKIM, DMARC) are correctly configured and aligned.

Common pitfalls

Ignoring low engagement metrics, as these can lead to silent filtering over time.

Sending to old or uncleaned lists, which increases the risk of hitting spam traps.

Focusing solely on bounce rates and spam complaints without considering other deliverability factors.

Making significant changes to email content or sending patterns without testing impact.

Expert tips

Always include a clearly visible and functional unsubscribe link to encourage unsubscriptions over spam complaints.

If listed on a major blocklist like Spamhaus, engage directly with their support team.

For deferred messages, understand your ESP's retry policy and how long until a bounce is recorded.

A/B test subject lines and content to improve open and click-through rates.

Expert view

Expert from Email Geeks says that an 80% delivery rate implies a 20% bounce rate, even if not immediately reported, because Sent minus Bounced equals Delivered. Some systems might show initial delivery until a bounce occurs after message expiration. This often happens with deferrals, where an ESP retries messages until a maximum time has passed, leading to a later influx of bounces.

2020-01-24 - Email Geeks

Expert view

Expert from Email Geeks notes that if a domain is listed on Spamhaus, it typically indicates issues such as bot sign-ups, using very old data, or sending to a purchased (and likely low-quality) list.

2020-01-28 - Email Geeks

Navigating unseen deliverability challenges

When your email deliverability inexplicably drops despite seemingly low spam and bounce rates, the problem often lies in less obvious areas like your sender reputation, engagement metrics, or hidden blocklist (blacklist) issues. It's crucial to look beyond surface-level metrics and delve into the nuances of how mailbox providers assess your sending practices.

By actively monitoring your reputation, meticulously cleaning your email lists, ensuring proper authentication, and optimizing your content and sending patterns, you can diagnose and rectify these underlying issues. Proactive management and a deep understanding of email deliverability best practices are essential to ensure your messages consistently reach their intended inboxes.