I'm a Linux administrator dealing with a frustrating issue related to Microsoft 365. We use MS365 solely for Teams, while our email is handled by an in-house Linux server. We've configured our MS365 settings so that the email addresses used in Teams belong to our own domain, not the onmicrosoft.com domain.
The problem arises when someone sends a Teams invitation. Emails sent to external domains are delivered without issues, but those sent to coworkers within our organization just seem to vanish. There are no error messages, and it's as if these emails are never even created or sent.
I did some digging and found that I might need to set up an outbound connector in the Exchange Admin Center to ensure these internal emails are routed correctly to our in-house mail server. However, even after creating this connector and a transport rule to forward messages intended for our domain, it still doesn't work. I'm feeling a bit lost—any ideas on how to fix this?
4 Answers
You might need to establish a send connector in your MS365 Tenant so that your Linux box acts as the outgoing SMTP relay for your domain. Have you set that up yet? It could help.
It sounds like the issue may not be with the emails actually being sent, but rather with how Microsoft routes them internally. If those users are recognized within your MS365 tenant, it could try to deliver them internally rather than hitting your MX server. You might consider setting them as external contacts or tweaking the internal resolution settings to enforce external routing.
I hear you, but our setup is actually saving us money. With 100 mailboxes and lots of data, the costs associated with maintaining a local server—even with backups—are way less than cloud alternatives. Plus, we have a solid spam defense in place. We're only on MS365 for Teams since it's what everyone else uses.
Have you thought about moving your email to the cloud? I remember managing my own email server and it was a constant battle with issues like spam. Nowadays, it's much easier managing it in the cloud, and you might find it more cost-effective, too.

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