While configuring Outlook mail client, the pop-up warning appears:
The target principal name is incorrect
When check the certificate via
View Certificate...it shows incorrect certificate:
This CA Root certificate is not trusted. To enable trust, install this certificate in the Trusted Root Certification Authorities store.
The correct SSL certificate is installed for Mail Server at Tools & Settings > SSL/TLS Certificates > Certificate for securing mail [change].
The secured mail server name is used in Outlook account settings as Incoming and Outgoing mail server names.
Go to Tools & Settings > SSL/TLS Certificates > Certificate for securing mail [change] and click Apply to re-apply the mail server certificate.