I have two problems:
1.) I'm trying to set up outgoing mails to customers for days. So it is not possible for me that the system sends emails. Also keien test emails are sent. I have specified an external host, password, port and user under Settings -> Platform -> System Emails. With the same credentials I can log in to my email account and send and receive emails, this works. Do I need to do anything else here? There are 2 roles installed: Application and Database.
2) I am trying to set up a mail server. I would like IMAP and SMTP to be the same for all domains so I can send customers simple instructions for email setup. Unfortunately, for the domain "mail.domein.tld" I cannot create a lets encrypt SSL - only the self-signed certificate. But this is not liked by the email client. Is there a solution here?