Access Denied | Zimbra Relay

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.

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. zimbra relay access denied

This most often happens in three specific scenarios: Zimbra’s default security stance is: Authenticate first, then relay. If a device or script tries to send mail through your server on port 25 (the standard SMTP port) without a username and password, Zimbra will reject it. If you manage a Zimbra Collaboration Suite (ZCS)