Since you mentioned this could you please give some hints on how to enable external forwarding at all? Spent hours on the issue last month before finally giving up deciphering the maze of the legacy UI. Thanks in advance.
Okay so step 1: you try to enable forwarding, but the UI gives you an error about some policy that has to be set
https://docs.microsoft.com/en-us/exchange/recipients-in-exch...
Step 2: you have to find the anti spam settings in a UI called „defender something“ and turn the automatic forwarding polic on.
https://docs.microsoft.com/en-us/microsoft-365/security/offi...
Again the UI doesn‘t allow this because some setting in your organisation is disabled.
Step 3: the hard part. This setting can only be disabled through powershell. Google the name of it and you will find some docs about it.
There might be other ways to achieve forwarding. At least it sounds like that in the docs, but then they must be buried deep below the legacy UIs.
Good luck!