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.
To test if this is the issue, try:
Start with authentication (port 587). If that doesn’t work, check your mynetworks . Nine times out of ten, that resolves the issue. zimbra relay access denied
Add the device’s IP address to Zimbra’s “mynetworks” setting. This tells Zimbra, "Trust anything coming from this IP." Change the sending device to use port 587
| 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. If that doesn’t work, check your mynetworks
zmprov modifyAccount [email protected] +zimbraAllowFromAddress [email protected] zmprov fc account [email protected] This is a classic "broken copier" or "buggy CRM" problem. Printers, scanners, and legacy applications often hard-code an IP address and try to send mail without logging in.
zmprov modifyServer `zmhostname` zimbraMtaMyNetworks '127.0.0.0/8 10.0.0.0/24 YOUR_DEVICE_IP/32' zmcontrol restart mta Only do this for internal, static IPs. Never add public IP ranges here. How to Diagnose the Problem in 30 Seconds Still stuck? Check the mail logs. SSH into your Zimbra server and run: