Mail is forwarding, but I don't know why

[bchase]

I'm working with an inherited setup: O365 with Azure AD used to tie into our local AD.

I have an address "service@mydomain.com" that is forwarding to a vendor at "old_service@external.com". I need to to forward to "new_service@external.com" instead, but I can't figure out where to make this change.

service@mydomain.com has no licenses assigned in o365 and so doesn't have a mailbox or forwarding rules, the user doesn't exist on our local AD server, it's not a distribution list or group, and I see no mail rules in Exchange admin center that would forward this user's mail, and we have no connectors set up. The user does show up in Azure AD, but I don't see anything related to mail forwarding (and don't expect to).

If I do a mail trace on this address, all mail statuses are "resolved" and I see this under "More information"

"Messages sent to the recipient are being forwarded to the following address.

External address: service@external.com"

Any ideas for how this thing could be set up?

[#2]

Hi, sounds like an outbound spam filter policy is configured. If not verified, you can go here.

https://protection.office.com/antispam

https://docs.microsoft.com/en-us/microsoft-365/security/office-365-security/external-email-forwardin...

[#3]

If you are getting results in message trace, you obviously have some recipient object for said address within the tenant. Use Get-Recipient to find the matching object and check its properties for forwarding. Running a Detailed message trace should give you some additional information as well (Get-MessageTraceDetail).