Can't search Explorer for MS Exchange for emails from internal domain

[HeebyGeeby]

I have a case open #06115580
I have created a test account/mailbox john.smith@mydomain.com, containing emails sent from a few different users/domains including gmail and my own domain.
If I search for emails from:user.name@gmail.com say, the emails are returned by the search as you'd expect.
If I search for emails from:user.name@mydomain.com, internal emails, nothing is returned.
The same is true if I use "From addresses is exactly" in Advanced Find.

I know there is an email from an internal user (me) to the test user, I can open it and view the headers which confirm it is From:user.name@mydomain.com
The mailboxes are MS 365. The same behaviour goes for all accounts in the domain, can't search for internal emails.
Nothing unusual in logs.

Could someone confirm it is possible to search for emails sent from an internal user, within the same domain?

[Mike Resseler]

Hi Geoff,

Yes, this certainly should be possible. Not sure why that doesn't work. Keep us informed about how the case goes. Our internal engineers will dive deeper into the logs and hopefully they figure out what is wrong. Just so I understood it correctly... If you open the Veeam explorer, you can actually see that email from the internal sender (without searching)

[HeebyGeeby]

Hi Mike

Correct, if I simply click on the inbox within Explorer, the email is there along with the others.
It's headers are slightly different to the gmail test email so I'll add headers from both to the support case.
It's possible there's a misconfiguration of our mailbox though it's 10 years old, MS 365 and should be fairly standard.

Rgds
Geoff