Question Setup postfix SMTP with domain alias

[Johnny9977]

I'm currently trying hard to get the Postfix on my Plesk running on my main domain because I want to use the installed SSL certificate there.

So in my case I've a webserver with a domain example.de which has a valid SSL certificate. I've created now a domain alias and only enabled E-Mail services. The alias is: mail.example.de.

After this I've edited the Postfix config file and replaced the hostname by my new domain alias. But when I ping this alias now I don't get any results. And also E-Mails don't get sent.

So what I've forgot here?