If Google Postmaster is showing "Not compliant" for Honor unsubscribes for a domain, it means that your mail server is not properly handling unsubscribe requests from users, and Gmail is detecting that some users who unsubscribed are still receiving emails from your domain. This can severely impact your IP reputation and email deliverability. Here are a few tips to prevent and fix such situations.

Unsubscribe process check

Ensure unsubscribes are processed immediately

• The unsubscribe link in your email must be functional and honoured in real time.
• Remove unsubscribed users from all future email lists immediately.
• Test the unsubscribe process to ensure users don’t receive further emails after opting out.

Regularly sync your suppression list

If you're using a third-party ESP (email service provider), make sure your suppression list is synced properly. Cross-check with Gmail’s feedback loops to identify users who marked emails as spam after unsubscribing.

Re-test and monitor compliance

Send test emails to your own Gmail accounts and unsubscribe to confirm that the process works. Monitor Google Postmaster regularly to see if compliance improves. By fixing this issue, you'll protect your sender's reputation and ensure better email deliverability.

Experience creation tips

Use Gmail’s list-unsubscribe header

Implement list-unsubscribe headers in your email to provide an easy opt-out method. Use both:

• list-unsubscribe-post (one-click unsubscribe)
• list-unsubscribe (email-based unsubscribe)

Implement a preference center

Instead of forcing a full unsubscribe, offer options like:

• reduce frequency (e.g. weekly instead of daily)
• choose specific topics of interest
• pause emails for a certain period

Monitor and fix complaints

Monitor the "spam rate" metric in Google Postmaster. If unsubscribed users continue to receive emails, they might mark them as spam, further damaging your reputation. 

Mailing list audit

Clean your mailing lists

• Remove historical unsubscribed users who might have been mistakenly re-added.
• Run a data validation check to clean old, non-engaged recipients.
• Remove old, non-existent, or inactive email addresses, as they can harm your IP reputation.

Segment your audience

Instead of sending emails in one go, break the list into 5-6 parts over a few days. This way, you can reach to up to 150,000 recipients in one send without triggering spam filters.