Hi,
Briefly.
We have a server sat within our organisation (virtual server - 10.10.10.111) that needs to accept emails that in turn are processed into invoices on a financial system.
We have mailboxes that sit on our on premise hybrid server that receive invoices from external senders that then forwards them to a custom domain/email address (test@invoice-test-contoso.co.uk)
We have a contact setup on premise with that email so it can be forwarded in that way (test@invoice-test-contoso.co.uk).
We then have a custom send connector setup that looks for any mail sent to the domain invoice-test-contoso.co.uk and forwards it to a smart host (10.10.10.111) which is the above mentioned virtual server.
The above process works perfectly fine. However;
When I move the mailbox to O365 and try to do the same thing, I get the error: Status code: 550 5.7.1
On O365 I have a remote domain setup that accepts forwarding as well as have forwarding turned on for the original domain of the external facing mailbox.
I have a connector setup to route mail to the on premise server name. (TLS with any digital cert)
I have a transport rule that says any mail that is sent to the domain of invoice-test-contoso.co.uk use the above connector - this should in theory mean that when the external facing mailbox (sitting in our O365 organization) forwards to test@invoice-test-contoso.co.uk - it should route the mail to the above connector which should then route the mail to our on premise hybrid server which should then deal with the mail accordingly, but it clearly doesn't.
I'm at a bit of a loss and need some advice. Mail flow theory;
Mail comes into external facing mailbox (o365) > forwards to test@invoice-test-contoso.co.uk > uses connector to route to smart host of on premise hybrid > should use send connector on premise to forward to virtual server
The custom domain invoice-test-contoso.co.uk doesn't exist anywhere. It is simply setup as a receive address on the virtual server. It isn't an owned domain and has never needed to be.
Cheers