Change mail server hostname

Hello,

I have the following Question:

I have two domains:
abc.de and xxxxx.de

All records of xxxxx.de are pointing to my Server IP including MX record etc...
Of abc.de there is only a MX record to mail.abc.de and a A record to my Server IP.
Other A records a pointing to a different IP.

The hostname of the server is server.xxxxx.de
For sending E-Mail I am using the hostname, because there is already the SSL certificate in postifx for server.xxxxx.de installed and working.

Now I got the Problem that one E-Mail provider rejects mails from my server because they say the hostname where the mails are coming from is not mail.xxxxx.de, but server.xxxxx.de

I've set up DMARC, DKIM and SPF and they are working.

Now in order to achieve this goal, do I have to create a new SSL cert. for mail.abc.de and change the mail server name in postfix?
Do I have to change the complete hostname of the server to mail.abc.de?

Or is it a bigger Problem that only mail.abc.de is pointing to a different IP than the other records?

I'm sorry for my lack knowledge but when it comes to hostname/server name things I can't really imagine this things.
I have already googled a few hours but I found no solution yet, probably it's very easy...

Kind regards

 

Set SPF to include the e-mail server (servers) that really sends the message.
Do you have one server? Set all domains MX to the e-mail server FQDN, and SPF to the sending e-mail server.
My signature has links to tutorials.

 

Thank you for your answer.

In the SPF Record is already the "v=spf1 a mx a:server.xxxxx.de ip4:...."

So since there is only one FQDN/one Server/IP for all services, I think I have to change the hostname completely to mail.abc.de in order to fulfill the weird requirements. ( postmaster.t-online.de/#t4.1 )** Not yet allowed to post Links

I think I will create a Website for mail.abc.de, to get a Let's Encrypt SSL cert.
Change the Hostname of the Server and Postfix to mail.abc.de and make a link from the website cert to the postfix cert.

 

ISPConfig sets up the hostname e-mail uses from the hostname (refer to the ISPConfig Perfect Server Guide). So what

Code:

hostname -f 

shows becomes the mailname.
If you do not want that, you can configure postfix to use some other mailname. It is in postfix configuration files. Then restart postix.

 

Alright, Thank you.
So and there is no constraint that postfix has to use the FQDN of the Server?