Unable to send email messages from the Plesk server: [552] Relay Denied: Failed to meet all relay criteria

Symptoms

• Unable to send email messages from the Plesk server with the following error in %plesk_dir%Mail Servers\Mail Enable\Logging\SMTP\SMTP-Debug-XX.log file:

  CONFIG_TEXT: [552] Relay Denied: Failed to meet all relay criteria. Attempt to relay to [SMTP:mailbox@example.com] was denied for requesting IP Address 203.0.113.2

Cause

The IP address 203.0.113.2 does not have relay rights.

Resolution

1. Log into the server via RDP.

2. Go to Start > MailEnable > Servers > Localhost > Services and Connectors > right click on SMTP  > Properties > Relay.

3. Enable the Allow relay for privileged IP ranges option and press the Apply button:
   
4. Press on the Privileged IPs button and in the next appeared window press the Add button.
5. Add the affected IP address 203.0.113.2 and select the Grated relay rights option:
   
6. Press the Close button and in the next appeared window press the OK button.