Office365 AUTH requests for ActiveSync Clients

trying to deploy APM SSO for Office365 and ran into a few issues, mostly on our side though. The latest issue is that it seems like Office365 removes the user's domain from the authorization request for ActiveSync clients, so when I look in the APM logs, I see failed attempts for "firstname.lastname" from Office365 instead of "firstname.lastname@mydomain.com." this wouldn't be an issue if our UPNs and email addresseses matched and we didn't have multiple email domains in our company. but in this case, our UPN and email address don't match and we have multiple domains that are being migrated to Office365. I have been able to get around this by adding a variable that adds "@mycompany" to the username, but that will not work once we start migrating other domains.

so my question is, has anybody else noticed that Office365 removes the user's domain from the request? or is there some misconfiguration on my side that is removing the user's domain?