Forward a Microsoft 365 address to Bosun
Use a transport rule or a distribution group — not user-level mailbox
forwarding. Microsoft blocks user-level auto-forwarding to external addresses by default,
and it fails with 550 5.7.520.
Route A — transport rule (works for any address)
Open
admin.exchange.microsoft.comand go to Mail flow → Rules.Add a rule: Apply to messages sent to your shared address.
Action: Bcc the message to your Bosun ingest address (e.g.
in-8f3a2c94@in.usebosun.com). Bcc keeps the original delivery untouched.Set the rule mode to Enforce and save. Rules take effect within about 30 minutes.
Route B — the address is a distribution group
In
admin.exchange.microsoft.com, open Recipients → Groups and select the group.Add the Bosun ingest address as a member (create it as a mail contact first if prompted).
Under group settings, allow external senders if customers email this address directly.
Careful: Don't use Outlook's own “Forwarding” setting on a user mailbox. Even when an admin
enables it, the tenant's outbound spam policy usually rejects it with
550 5.7.520 Access denied, Your organization does not allow external forwarding
— the fix for that error is
here, but a transport rule avoids
the whole problem.
Check it worked: Send a test email to the shared address. Bosun's setup screen is watching live and flips to “arrived” when the rule fires. If nothing arrives in 30 minutes, the rule probably hasn't propagated yet — Microsoft is slower than Google here.
Still not working?
Message trace (Mail flow → Message trace) shows exactly what Exchange did with your test
email — look for the Bcc action. If the trace shows a 550 bounce to the
ingest address, match the code against our
fixes index.