Can not set up a mail client for the mailbox from Plesk: The target principal name is incorrect

Symptoms

• When manually setting up a mail client, for example, Microsoft Outlook, the warning message appears:

  CONFIG_TEXT: The server you are connected to is using a security certificate that cannot be verified.
  The target principal name is incorrect
  Do you want to continue using this server?

  

• Pressing the "View Certificate" button shows that the mail client uses a default mail server certificate installed in Tools & Settings > SSL/TLS Certificates > Certificate for securing mail.

• A separate certificate for securing mail server is selected for the domain in Domains > example.com > Mail Settings > SSL/TLS certificate for mail.

Cause

The incorrect hostname is used as Incoming/Outgoing mail server when setting up the mail client.

When securing a mail server with a separate mail certificate, only mail domains below are secured:

• example.com

• mail.example.com

Resolution

Set up mail client using 'example.com' or 'mail.example.com' as Incoming/Outgoing mail server.