I currently have a customer (COMPANY) who has to (by contract) use the IMAP mailboxes provided by their business partner (PARTNER). On the other hand, they want to use MS Exchange (which PARTNER does not offer) via the Office 365 business essentials product.
So the basic and obvious idea was to ask PARTNER to forward their mail (sent to email@example.com) to COMPANY's own addresses (firstname.lastname@example.org) instead of storing it in the IMAP mailboxes previously mentioned.
The problem seems to be on the outgoing side. I have looked into this in a test setup a little and I don't see any way to either
- configure Exchange so it accepts and sends outgoing mail with the email@example.com mail address (I'm receiving a delivery failure notification indicating I don't have permission to "send via the specified user").
- configure Outlook clients so they send outgoing mail via partner.com 's MX server instead of via it's own infrastructure (there's no such setting).
So (how) can this be done at all?
COMPANY has full DNS control for company.com but of course not for partner.com.