Email Sending Health: Maintaining Great Rates & Recovering When Things Go Wrong

The Three Metrics That Matter

All three metrics are monitored continuously. Even a short spike can affect your sending health, so it's best to build good habits from the start rather than react after the fact.

Bounce Rate — Keep It Below 2%

There are two types of bounces:

• Hard Bounce: The email address does not exist, the domain is invalid, or the recipient's server permanently rejected the email.
• Soft Bounce: A temporary issue — the inbox is full, the server was down, or the message was too large. These can resolve on their own but repeated soft bounces become a problem.

1. Use a verified opt-in process — only email people who confirmed their address
2. Never import purchased or scraped lists — these almost always contain invalid addresses
3. Regularly clean your contact list — remove addresses that have not engaged in 6+ months
4. Use an email verification tool before importing large lists
5. Remove hard bounces immediately after each campaign — do not retry them
6. Avoid sending to role-based addresses like info@, admin@, noreply@ — these bounce frequently

1. Stop sending campaigns to your full list immediately
2. Export all contacts who have bounced and permanently suppress them
3. Run your remaining list through an email verification service to identify other at-risk addresses
4. Remove or suppress any address that hasn't opened an email in the last 90 days
5. Resume sending to your most engaged segment only — those who opened in the last 30 days
6. Gradually expand back to your broader list only after bounce rate returns below 2%

• Hard bounced addresses should be permanently suppressed.
• Re-sending to them signals poor list hygiene to inbox providers and will worsen your sending health.
• The platform automatically suppresses hard bounces — do not manually re-add them.

Spam Complaint Rate — Keep It Below 0.1%

• Recipients do not remember signing up or did not consent to receive emails
• Email content feels irrelevant, unexpected, or too frequent
• The unsubscribe option is hard to find or does not work properly
• Emails look like phishing or are overly promotional in tone
• Sending to old lists that were not engaged for a long time

1. Always get explicit consent — never assume opt-in
2. Send a clear welcome email immediately after someone subscribes so they recognise your name
3. Make the unsubscribe link large, visible, and working in every email
4. Set expectations upfront — tell subscribers what kind of content they'll receive and how often
5. Respect unsubscribe requests immediately — never delay removal
6. Avoid subject lines that feel deceptive, overly salesy, or misleading
7. Match the email content to what the subscriber originally signed up for
8. Reduce frequency if engagement is dropping — over-sending is a leading cause of complaints

1. Pause all bulk email campaigns immediately — even a few more complaints will worsen the situation
2. Identify which campaigns or segments are generating the most complaints
3. Suppress everyone who complained — do not email them again
4. Review your opt-in flow to ensure consent is genuine and clear
5. Rewrite subject lines and email content to be less aggressive or misleading
6. Add a highly visible one-click unsubscribe to every email going forward
7. Resume sending only to your most engaged subscribers — people who opened in the last 30 days
8. Monitor complaint rate daily until it returns below 0.1%

• Gmail treats a complaint rate above 0.08% as a warning and above 0.1% as critical.
• Yahoo Mail applies similar enforcement policies.
• Sustained high complaint rates can result in your emails being bulk-foldered or blocked entirely.

Open Rate — Keep It Above 15%

• Subject line: The single biggest factor — unclear or generic subject lines dramatically reduce opens
• Sender name: Recipients open emails from names they recognise and trust
• Send time: Emails sent at the wrong time for your audience will be buried or ignored
• List quality: Disengaged contacts drag the open rate down — even if your content is great
• Preview text: The short text shown next to the subject line in the inbox — often overlooked but influential

1. Write subject lines that are specific, curiosity-driven, or clearly valuable — avoid clickbait
2. Personalise the subject line with the recipient's first name where appropriate
3. Keep subject lines under 50 characters so they don't get cut off on mobile
4. Write a compelling preview text that complements the subject line
5. Send from a consistent, recognisable sender name — not a generic address
6. Test different send times — for most audiences Tuesday–Thursday between 9am and 11am performs well
7. Segment your list and send content that is relevant to each group
8. Re-engage or remove inactive subscribers regularly to keep your active list healthy

1. Do not send to your full list — this will make the open rate worse, not better
2. Identify your most engaged segment — contacts who opened at least one email in the last 60 days
3. Send a targeted re-engagement campaign to inactive contacts with a compelling offer or question
   • Example: "Are you still interested in hearing from us? Click here to stay subscribed."
4. Remove or suppress contacts who do not engage with the re-engagement campaign
5. A/B test 2–3 different subject lines on a small segment before sending to your full list
6. Review your email frequency — if you send too often, engagement drops
7. Once open rate recovers above 15%, gradually expand sending to a broader audience

Open rate is also affected by Apple Mail Privacy Protection (MPP), which pre-loads emails and registers them as 'opened'. If a large portion of your audience uses Apple Mail, your open rate may appear higher than actual engagement. Focus on click rate as a secondary signal.

Prevention Checklist — Best Practices at a Glance

Quick Recovery Reference

Frequently Asked Questions