Acting as smtp for non-hosted domain

Hi,
I have a domain X that is not dns controlled by my MiAB box. Mail sent to this domain are all forwarded to another domain Y which is on my MiAB. When I reply to one of these mails, I would like to use my MiAB as smtp server. This works mostly by setting domain X as alias for one of the email addresses on domain Y. There is however one problem. When I get a mail from an address on domain X and reply to it, then MiAB (correctly) state that this email address is not in the virtual users table and hence it cannot sent to it (basically MiAB sees domain X as belonging to itself).
Is there a way I can tell MiAB that this domain is on a different server or somehow make it always forward mails to domain X to another mail server?

Remove the alias … and forward mails to domain X somewhere else other than domain Y.
Wouldn’t it be easier to just handle email for domain X on the MiaB?

Let me ask you this … is domain X basically an alternative domain name for domain Y? If so, why aren’t you using a ‘Domain Alias’ in MiaB instead? Please do describe the actual scenario in detail so that I can help you determine a solution.

Not that easy.
Domain X is a family domain with a lot of users where most of them use the defective mail solution from the hosting provider. I have all my mails handled via MIAB and hence I forward all my mails from domain X to a domain on my MIAB box.
I am not i a position to move domain X to my MIAB nor am I willing to use the mail service provided by the hosting company (they have way too little mail box size + they only provide pop3).

Sounds like a great opportunity to convince them to switch to a proper email service! :stuck_out_tongue:

So back to your situation. Why not simply use their SMTP server for the outbound email? Do you demand to use webmail, or does domain X’s mail server? You can only accomplish this with a desktop or email client - or webmail client installed externally to MiaB.

There is no solution that is not an unsupported modification to MiaB. To accomplish your goal with the limitation you have you will need to configure postfix to handle that specific domain differently.

Explain why it is most, not all. Or are you the exception?

Probably the simplest suggestion is to host your personal emails on a subdomain which is hosted on the MiaB. Your email address will be me@kimusan.familydomain.tld. When an email is received by you and you need to reply to someone@familydomain.tld, then there should be no issue. This method also eliminates the ‘defective mail solution’ completely as far as you are concerned. This would require you to have access to the DNS records of the domain to set a NS record pointed to your MiaB. And the domain needs to be registered with a registrar whose DNS is smart enough to accomplish this…

And if changing your personal email address is too much of a hassle, continue to have mails sent to you@familydomain.tld - then forward them to you@kimusan.familydomain.tld and reply always from you@kimusan.familydomain.tld. Eventually you can make the old email address go away, or not. Basically, this should be your domain Y.