Zimbra Relay Access Denied -

It usually appears without warning. One minute, a user or an application is sending mail fine; the next, emails are bouncing back. Don’t panic. This error is actually Zimbra’s security system doing its job—it just needs a little adjustment.

If you manage a Zimbra Collaboration Suite (ZCS) environment, you’ve likely seen the dreaded "554 5.7.1 <[email protected]>: Relay access denied" error in your mail logs. zimbra relay access denied

| Setting | Command to Check | Desired State | | :--- | :--- | :--- | | | zmprov getServer zimbraMtaTlsAuthOnly | TRUE | | Submission Port | zmprov getServer zimbraMtaAuthEnabled | TRUE on port 587 | | Trusted Networks | zmprov getServer zimbraMtaMyNetworks | Only internal subnets | Final Thoughts "Relay access denied" is frustrating because it stops legitimate email. But remember: without this guardrail, your Zimbra server would be an open relay—and it would be blacklisted within hours. It usually appears without warning

Change the sending device to use port 587 (Submission) instead of port 25, and enable SMTP Authentication . Most modern email clients (Outlook, Thunderbird, Apple Mail) support this natively. This error is actually Zimbra’s security system doing

Add the external domain to the list of allowed "From" addresses:

Start with authentication (port 587). If that doesn’t work, check your mynetworks . Nine times out of ten, that resolves the issue.

In this post, we’ll break down why this happens and the three most common ways to fix it. An SMTP relay is when a mail server accepts a message and delivers it to a domain that is not its own.