Question Outgoing mail problem

[Cherimos]

Dear Plesk Community,

This is going to be my first question because I can't find a clear answer for my problem on the board/internet.

I have a server which almost al domains can't send emails without getting any errors.
Error Message: " This is the mail system at host cust123.localdomain.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster."

When I test the email on Newsletters spam test by mail-tester.com I get the an error on the next line:
We didn't find a server (A Record) behind your hostname cust123.localdomain.

When I check my settings, Tools & Settings > server settings
I see the next hostname cust123.phillahost.com which is correct.

Does somebody know the anser for my problem?
Thanks in advance.

 

[IgorG]

We didn't find a server (A Record) behind your hostname cust123.localdomain.

This is related to DNS settings. You need to check DNS records for your domain. Make sure that you have corresponding A record for this domain.