Tank you very much for your reply - probably my question lacks information somehow. Though at the moment i can´t even test DKIM signing throughout problem getting a single mail on an alias out to the world. (Smartermail 16)
Maybe some more or detailed information helps on solving my problem.
We´ve one Smartermail Gateway, let´s call the domain gateway.com. On there there a several domains called 001.gateway.com, 002.gateway.com and so on. On every of those there´s a single User configured, e.g. firstname.lastname@example.org.
Those accounts are accessed from Debian Postfix SMTPs to relay out on local configured Mailadresses from CMS oder Shops eg. email@example.com. So the Postifx uses Auth to send out Mails from non specified email names on one domain.
Those mail adresses could be anything, we don´t know though our customers define those themselves.
What we are doing now is to add the DomainAlias customer.com to one of the defined gateway.com Domains.
The postfix get´s the relay account to relay, but this won´t work out, though Smartermail checks if the used Adress is a local adress on the Usertable of the Domain Alias. It is not, as we don´t know the adresses.
So right here lies our problem at the moment - if we could solve this one, for sure your DKIM setting will work out.
Thanks for your help.
Best wishes, Norman