Hostname mismatch warnings appear when the mail client connects to a hostname that is not covered by the certificate presented by the server.
Common symptoms
- Outlook or mobile mail warns about certificate mismatch
- Mail still works but users see trust warnings
- Using the domain name causes a warning while another hostname does not
Troubleshooting steps
- Compare the mail server hostname recommended in your hosting details with the hostname configured in the client.
- Use a hostname that matches the installed certificate, especially during initial setup.
- If you prefer branded mail hostnames, confirm the required DNS and SSL are in place first.
- Do not instruct users to ignore certificate warnings permanently in production.
- Retest both incoming and outgoing mail after correcting the hostname.
Additional notes
- During migrations, old server names are often left in client configs.
- Using the same hostname for both IMAP and SMTP simplifies client setup and certificate trust.
When to contact support
Contact support if you need the correct service hostname for secure mail configuration.