A mail certificate warning concerns the server your application is connecting to. Compare that configured server name with the certificate it presents, and keep certificate validation enabled while the mismatch or trust problem is corrected.
01 Collect and correct the connection details
- Record whether the warning occurs when receiving, sending or opening webmail. Note the server hostname, port, security mode and exact warning.
- Compare the configured hostname with the current settings supplied for your actual email product. OX, Google Workspace, Zoho and hosting-panel mail can use different endpoints.
- Check the certificate's name coverage, validity and issuer. Have support investigate an unexpected certificate rather than accepting it permanently.
- If you administer an eligible Plesk mail service, review the domain under Mail > Mail Settings. The certificate for mail and the certificate for webmail are separate assignments where the server supports them.
- If the service requires a provider server hostname, use that documented name instead of inventing
mail.example.com. A DNS alias does not extend the target certificate's coverage. - Retest receiving and sending, then webmail separately. Record the corrected settings for other affected devices.
Common questions
Why does my website's certificate not fix Outlook?
The website and IMAP or SMTP service can run on different endpoints and present different certificates. Identify the actual connection showing the warning.
Does TLS encrypt the message forever?
Transport encryption protects a particular connection. It is different from message-level encryption and from the recipient's storage or access controls.
Can an old device cause the warning?
An outdated trust store, incorrect clock or unsupported software can contribute. Check the device date and updates, but investigate the server certificate too, especially if several current devices fail.