- Plesk for Linux
A record for mail.example.com in Domains > example.com > DNS Settings of subscription points to the private IP 192.0.2.2 instead of the public one 203.0.113.2.
In Mail Server Settings > Outgoing mail mode is set to Send from the specified IP addresses > 192.0.2.2
A proper mapping of these IP addresses is set up in Tools & Settings > IP Addresses section: a public IP is assigned to a private IP.
This is caused by a Plesk bug with the ID # PPPM-10418 which will be fixed in future product updates.
As a workaround:
Go Tools & Settings > Mail Server Settings.
Change Send from domain IP addresses to None in the section Outgoing mail mode.
Open DNS Settings of subscription and press Apply DNS Template button.