Troubleshooting Email Deliverability Issues
Troubleshooting Email Deliverability Issues
Purpose: When deliverability problems show up, a systematic approach helps you figure out what’s happening and take the right corrective action. This article walks through the key diagnostic questions and what to do at each step.
Before You Begin
This article covers diagnosing and recovering from deliverability problems after they’ve appeared. For prevention, see Managing List Health: Sunsetting and Engagement, Email Authentication: SPF, DKIM, and DMARC, and Email Compliance and Permission Best Practices.
Senders with access to the Sure Send Deliverability Suite have additional diagnostic tools available, noted below where relevant.
Step 1: Are Your Messages Being Delivered?
Start with your delivery rate. A delivery rate below 90% is a strong sign that a meaningful share of your messages are being rejected before they reach the recipient.
How to Check Bounce Data
Reading Bounce Reasons
| What You See | What It Likely Means |
|---|---|
| Non-existent accounts, full inboxes, small numbers | Normal. Expected on any list over time. |
| Non-existent accounts, full inboxes, large numbers | Your list may be old or need cleaning. |
| “Spam,” “content,” “blocked,” “blocklisted,” “blacklisted” | A sending reputation problem. Contact your email provider to investigate further. |
Step 2: Are Delivered Messages Reaching the Inbox?
If your delivery rate looks healthy, the next question is whether messages are being filtered to spam instead of landing in the inbox.
Open rates are an imperfect but useful signal. Because many mailbox providers now trigger open events automatically (Apple Mail Privacy Protection is the most common example) before a recipient actually opens a message, it’s rare to see open rates below 30% when most of your mail is reaching the inbox. This isn’t a hard rule, but a significant drop below that at a specific provider is worth investigating.
Comparing Providers
If you have access to the Sure Send Deliverability Suite, it can break down delivery, open, and click rates by mailbox provider, which is the fastest way to tell whether a filtering problem is isolated to one provider.
Example: If open rates are 40-50% at most providers but only 10% at Gmail and 4% at Outlook, those two providers are likely filtering your messages to spam. That’s where to focus your investigation.
Step 3: Correcting the Problem
To recover from a deliverability issue, you need to rebuild mailbox providers’ confidence in your sending. The most effective way to do that is to temporarily limit your sends to your most engaged recipients only.
Sending to a tighter, highly engaged audience:
- Reduces spam complaints
- Improves the engagement ratios mailbox providers evaluate
- Stops the pattern of low engagement that caused the problem
As your metrics recover (delivery rates stabilize, open rates return to normal), gradually expand your audience again.
How to Identify Your Most Engaged Recipients
Build a Smart List using Last Email Opened and Last Email Clicked to isolate recipients who’ve engaged recently (see Smart List Filters: Field Reference). Target that list until your deliverability metrics recover. Senders with access to the Deliverability Suite can use its pre-calculated engagement data for more precise targeting. See Managing List Health: Sunsetting and Engagement for the full walkthrough.
Tips
iNote: If bounce reasons reference spam, content filtering, or blocklisting, don’t keep sending at full volume while you investigate. Continuing to send to the same audience compounds the problem. Scale back immediately and focus on your most engaged recipients while you diagnose the root cause.
iNote: Deliverability recovery takes time. Mailbox providers update their assessment of you gradually. Consistent, clean sending to an engaged audience over several weeks is what typically moves the needle, not a single campaign.