Deactivate mail.domain.tld aliases

I have installed ssl with the letsencrypt module for my complete server. So the server certificate is created for my hostname,so far so good. But all my mail client softwares show errors with the certificate because its not the mail servers adress they found. Instead its the hostname. Especially in the Gmail app on android this is a huge point.

The best and cleanest way, i think, would be to disable the mail.domain.tld aliases and instead add the hostname to the config. But how can i do this? Or is there a simpler and better way?

Thanks so far Helias10