So i have to use a shared domain during migration from
Zimbra to O365.
MX points to
Zimbra, but is also configured to enable outgoin emails from O365 to the world in the same domain. I've configured a connector on O365 to the zimbra (it works), and created contacts for not-yet-migrated users.
The plan is, that during migration, the incoming mail comes to zimbra and is redirected to O365 to onmicrosoft domain, for migrated users.
When i send email from O365 to anywhere (except my domain) it works correctly. When I send to anyone within company, that is still on zimbra, I get either of the errors:
550 5.7.1 ... Relaying denied 553 5.7.1 : Sender address rejected: not logged in
Zimbra clearly blocks my user, as it already exists within its server, but I don't know, where to start to unlock it? I've done similar things with other services before, but most didn't care about that.