If Mail can’t verify a server or a signature, you can review its certificate and then trust and accept it.
- In the "Verify Certificate" dialog, click "Show Certificate".
- Review the certificate and, if you have confidence in the server or signature, click the checkbox to always trust the certificate or to acknowledge the signature is valid.
- Click Connect or OK, and enter your account password, if prompted.
If the certificate is a root certificate, you must enter the name and password of an administrator of the Mac you’re using.
If you want to change a certificate’s trust policy later, you can use Keychain Access.
