Warning in mail client during connection to mailbox located on Plesk server: This site attempts to identify itself with invalid information

Symptoms

• When connecting to a mailbox john.doe@example.com using a mail client the following warning is shown:

  CONFIG_TEXT: The certificate for this server is invalid

  ---

  CONFIG_TEXT: certificate belongs to a different site, which could mean that someone is trying to impersonate this site

  ---

  CONFIG_TEXT: The target principal name is incorrect

  ---

  CONFIG_TEXT: Mail can't verify the identity of the server "mail.example.com".

  ---

  CONFIG_TEXT: stream_socket_client(): Peer cartificate CN='example.com' did not match expected CN='example.org'

  ---

  CONFIG_TEXT: Certificate subject and hostname mismatch

• The error shows that the certificate from the error belongs to serverhostname.com.

• Certificate in Tools & Settings > SSL/TLS Certificates > Certificate for securing mail is set to serverhostname.com.

Cause

Incorrect configuration of the mail client - mail server hostname does not match the one secured with a certificate.

Resolution

For Plesk Onyx:

Configure a mail client following the article.

For Plesk Obsidian:

Secure the mail server for domain according to the instructions from the article.