Plesk email notifications are not delivered through SMTP relay: not accepted due to 550-5.7.1 domain's DMARC policy

Symptoms

1. Email notifications (e. g. about scheduled tasks) are not delivered to remote mailbox.
2. Plesk notifications are sent from exampleserver.com
3. Plesk mail server is configured to use example.net as SMTP relay.
4. Error in /var/log/maillog:
   

   CONFIG_TEXT: postfix/qmgr[3743]: B9F7E30001FD: from=root@example.com, size=992, nrcpt=1 (queue active)
   in.l.exampleserver.com[203.0.113.2]:25, delay=5, delays=0.02/3.5/1.1/0.41, dsn=5.7.1, status=bounced (host smtp-in.exampleserver.com[203.0.113.2] said: 550-5.7.1 Unauthenticated email from example.net is not accepted due to 550-5.7.1 domain's DMARC policy. Please contact the administrator of 550-5.7.1 example.net domain if this was a legitimate mail. 

Cause

exampleserver.com is not configured to use example.net mailbox as return-path address.

Resolution

Note: specify actual mail addresses in the configuration directives below

1. Connect to Plesk server using SSH
2. Add the following line to the bottom of /etc/postfix/main.cf:
   

   CONFIG_TEXT: smtp_generic_maps = hash:/etc/postfix/generic

3. Create /etc/postfix/generic with the following content:
   

   CONFIG_TEXT: root@example.com support@example.net

4. Generate address map:

   # postmap /etc/postfix/generic

5. Restart Postfix:

   # service postfix restart