When sending mail to your server, the following error is produced:
SSL verify error: certificate name mismatch
More specifically, the error follows this format:
[server-ip] SSL verify error: certificate name mismatch: DN="/CN=server.hostname.com" H="mail.user-domain.com"
This warning, introduced in Exim 4.86, is a warning generated due to how Exim handles SNI. This is not an indication of an issue. The provided SSL report in the logs is a warning from the validation system within Exim. By default, this is only a warning and will not impede mail delivery.