How to share a SMTP domain between MDaemon and Exchange?

I need to setup coexistence between MDaemon (13.0.5) and a Microsoft Exchange system (Office 365); the two systems should share the same SMTP domain, and each one should forward to the other any message which has a recipient in that domain but is not local to the server; I already have safeguards in place against routing loops (using a custom header), so this is not an issue.

I have succesfully configured Exchange to route to MDaemon all messages which it can't deliver to its own mailboxes; this works without problems. Now I need to do the same on the MDaemon side.

I configured the relevant options in the "unknown mail" configuration section, but MDaemon keeps rejecting these messages with a 550 error (unknown user).

What am I missing here?

Solution 1:

Answer found: you need to configure MDaemon to accept messages addressed to (or coming from) unknown local users, which are by default refused: http://help.altn.com/mdaemon/en/index.html?security__relay_settings.htm.

Account Verification

SMTP MAIL address must exist if it uses a local domain

Click this option is you wish to verify that the MAIL value passed during the SMTP process points to an actual valid account when it is purported to be from a local domain or gateway.

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SMTP RCPT address must exist if it uses a local domain

Click this option is you wish to verify that the RCPT value passed during the SMTP process points to an actual valid account when it is purported to be from a local domain.