Cloud-based scanning

[Denis Beauchemin]

Hello,

We are about to move our MX to the cloud in Microsoft 365. The way it would work would be to scan the emails there and then deliver them to our servers.

The problem is that we can't for the moment tell MS365 which email addresses are valid and which are not (the data is in an LDAP server that is not synchronized with our AD). Thus MS365 will be forwarding all harmless emails to our internal servers who will reject invalid email addresses.

I seem to remember this is really not a good idea but I can't remember why. Can someone shed some light on this please? 

Thanks.

Denis