Hi there @meike297,
Thanks for sharing your website domain. I can confirm the domain is successfully authenticated and there are no issues on your account.
This is most likely an issue that happens when MailPoet’s scheduled key-validation task sees a different URL than the one your API key is registered to. Even though your key is valid on your MailPoet.com account, the cron task on your site may be resolving a slightly different URL (e.g., www vs. non-www, or an internal hosting URL), which causes the key to fail and sending to pause. The sender email becoming unauthenticated is a side effect of the key being invalidated.
Here’s how to track down and fix it:
Step 1: Enable logging to capture the mismatch
Go to MailPoet → Settings → Advanced → Logging and set it to “Everything”. Then wait for the error to reoccur. Once it does, go back to MailPoet → Settings → Advanced and click “View Logs”. Look for entries labeled mss.ERROR: key-validation.failed — expand the truncated message (Cmd+click on Mac, Ctrl+click on Windows) and it will show you which URL was returned during the failed check. That’s the key clue.
Step 2: Check for URL inconsistencies
Compare the URL in the failed log entry against your actual site URL. Common causes:
- A mismatch between the WordPress Address and Site Address in Settings → General
WP_SITEURL or WP_HOME constants set in your wp-config.php that differ from the database values — these constants also need to be defined before the line that loads wp-settings.php, otherwise cron may use an outdated database value- A
www vs. non-www discrepancy
- Your hosting provider triggering cron from an internal URL that differs from your public domain
Step 3: Apply a workaround while you investigate
Switching to server-side (Linux) cron bypasses the WordPress HTTP-based cron entirely, which avoids the URL mismatch during the key check. You can set this up by following this guide: https://kb.mailpoet.com/article/257-setting-the-server-side-cron-linux-cron
If you’re unsure how to set up a cron job, your hosting provider’s support team can usually help with this — just share the guide above with them.
Step 4: Re-authenticate your sender email
Once the key stays valid after the changes, go to MailPoet → Settings → Basics and re-verify your sender email authentication. It likely reset when the key was invalidated.
For more details, this MailPoet KB article covers the issue in depth: https://kb.mailpoet.com/article/398-what-should-i-do-if-my-mailpoet-key-is-deactivated-on-its-own
