Email sending health: how to keep rates healthy and recover when things go wrong

Table of contents

1. The three metrics that matter
2. Bounce rate: keep it below 2%
3. Causes: what makes emails bounce?
4. How to keep the bounce rate low
5. How to recover if the bounce rate is high
6. Warning: never send again to addresses that have hard bounced
7. Spam complaint rate: keep it below 0.1%
8. Causes: what triggers spam complaints?
9. How to keep the spam complaint rate low
10. How to recover if the complaint rate is high
11. Gmail and Yahoo now enforce strict complaint thresholds
12. Open rate: keep it above 15%
13. Factors: what affects the open rate?
14. How to keep the open rate high
15. How to recover if the open rate drops below 15%
16. Prevention checklist: best practice at a glance
17. Quick recovery guide
18. Frequently asked questions (FAQ)

The three metrics that matter

The health of your email sending is determined by three key metrics that mailbox providers use to judge whether your emails are wanted and, as a result, whether to deliver them. Keeping these metrics within healthy ranges makes sure your emails reach your contacts' inboxes instead of their spam folders.

This guide explains what each metric means, how to keep them in good shape and, if they do deteriorate, how to recover.

Mailbox providers continually assess your sending against these three benchmarks:

Tip: all three metrics are monitored continually. Even a short-lived spike can affect your sending health, so it is better to build good habits from the start than to react after the event.

Bounce rate: keep it below 2%

Causes: what makes emails bounce?

There are two types of bounce:

• Hard bounce: the email address does not exist, the domain is invalid or the recipient's server has permanently rejected the email.
• Soft bounce: a temporary problem, such as a full mailbox, a server that is down or a message that is too large. These issues can resolve themselves, but repeated soft bounces become a problem.

How to keep the bounce rate low

1. Use a verified opt-in process: only email people who have confirmed their address.
2. Never import purchased or web-scraped lists, as they almost always contain invalid addresses.
3. Clean your contact list regularly, removing addresses that have not engaged in the last 6+ months.
4. Use an email verification tool before importing large lists.
5. Remove hard bounces immediately after every campaign and do not try to send to those addresses again.
6. Avoid sending to role-based addresses such as info@, admin@ and noreply@, as they tend to bounce frequently.

How to recover if the bounce rate is high

1. Stop sending campaigns to your whole list immediately.
2. Export every contact that bounced and add them to a permanent suppression list.
3. Run your remaining list through an email verification service to identify other at-risk addresses.
4. Remove or suppress any address that has not opened an email in the last 90 days.
5. Only resume sending to your most engaged segment, meaning those who have opened an email in the last 30 days.
6. Gradually expand sending to the rest of the list only once the bounce rate is back below 2%.

Warning: never send again to addresses that have hard bounced

• Addresses that hard bounce should be suppressed permanently.
• Sending to those addresses again signals poor list hygiene to mailbox providers and will make your sending health worse.
• Futuria CRM suppresses hard bounces automatically: do not add them back manually.

Spam complaint rate: keep it below 0.1%

Causes: what triggers spam complaints?

• Recipients do not remember subscribing or did not consent to receiving emails.
• The email content is perceived as irrelevant, unexpected or too frequent.
• The unsubscribe option is hard to find or does not work properly.
• The emails look like phishing or have an overly promotional tone.
• You are sending to old lists that have not engaged for a long time.

How to keep the spam complaint rate low

1. Always obtain explicit consent; never assume opt-in.
2. Send a clear welcome email straight after sign-up, so recipients recognise your name.
3. Make the unsubscribe link large, visible and working in every email.
4. Set expectations from the outset: tell subscribers what kind of content they will receive and how often.
5. Honour unsubscribe requests immediately; never delay removal.
6. Avoid subject lines that look deceptive, overly commercial or misleading.
7. Make sure the email content matches the reason the person subscribed.
8. Reduce your frequency if engagement is dropping: sending too often is one of the main causes of complaints.

How to recover if the complaint rate is high

1. Pause all bulk email campaigns immediately: even a few more complaints will make the situation worse.
2. Identify which campaigns or segments are generating the most complaints.
3. Suppress everyone who complained; do not send any more emails to those contacts.
4. Review your opt-in process to make sure consent is genuine and clear.
5. Rewrite your email subject lines and content to make them less aggressive or misleading.
6. Add a prominent one-click unsubscribe link to every future email.
7. Only resume sending to your most engaged subscribers, meaning the people who have opened an email in the last 30 days.
8. Monitor the complaint rate daily until it is back below 0.1%.

Gmail and Yahoo now enforce strict complaint thresholds

• Gmail treats a complaint rate above 0.08% as a warning and above 0.1% as critical.
• Yahoo Mail applies similar enforcement policies.
• High, prolonged complaint rates can send your emails straight to the spam folder or have them blocked altogether.

Open rate: keep it above 15%

Factors: what affects the open rate?

• Subject line: the single most important factor. Unclear or generic subject lines cut opens dramatically.
• 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: unengaged contacts drag down your open rate, even when your content is excellent.
• Preview text: the short text shown next to the subject line in the inbox, often overlooked but influential.

How to keep the open rate high

1. Write subject lines that are specific, spark curiosity or offer clear value. Avoid clickbait.
2. Personalise the subject line with the recipient's name where appropriate.
3. Keep subject lines under 50 characters so they are not cut off on mobile devices.
4. Write 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 to Thursday between 9am and 11am performs well.
7. Segment your list and send relevant content to each group.
8. Regularly re-engage or remove inactive subscribers to keep your active list healthy.

How to recover if the open rate drops below 15%

1. Do not send to your whole list: that will make the open rate worse, not better.
2. Identify your most engaged segment: contacts who have opened at least one email in the last 60 days.
3. Send a re-engagement campaign to inactive contacts with an offer or an interesting question.
   • Example: "Do you still want to hear from us? Click here to stay subscribed."
4. Remove or suppress the 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 the whole list.
6. Review your sending frequency: if you send too often, engagement falls.
7. Once the open rate is back above 15%, gradually expand sending to a wider audience.

Tip: Apple Mail Privacy Protection
The open rate is also affected by Apple Mail Privacy Protection (MPP), which pre-loads emails and records them as "opened". If a large share of your audience uses Apple Mail, your open rate may look higher than actual engagement. Focus on the click rate as a secondary signal.

Prevention checklist: best practice at a glance

Quick recovery guide

If a metric deteriorates, use this table to act quickly:

Frequently asked questions (FAQ)