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[mrmarkuz (Markus Neuberger)]

You may try this:

Customizable Postfix SMTP banner host

The default SMTPD banner in Postfix is $hostname ESMTP $mail_name, which normally translates to something like <your_host_name> ESMTP Postfix. If the internal server name does not match the public DNS, the SMTP shows a hostname which may be incorrect, and make some email services reject messages or mark them as SPAM. It would be useful to have a way to override the default Postfix smtpd_banner configuration option. This can be done as easy as including a new template snippet named /etc/e-smit…

or this:

http://docs.nethserver.org/en/v7/mail.html#custom-helo