Hybrid Configuration delivery o365 to on-premise & Licence

Hello,

I have an hybrid configuration working. I can migrate on-premise to 365 and 365 to On-premise.

But I have an issue with the send & receiving mails. The mail flow connector works fine and AD user are syncronized 

The exact issue is. For example:

User1: On-premise account

User2: O365 account

When I send an email from user1 to user2 all works fine, mailbox o365 receive the mail

When I send an email from user2 to user1 the mail arrive to the o365 mailbox ,but the user has not migrated yet.

I've noticed that when user1 not have office365 license account assigned the mail flow is right, but I need to keep the user licence active because we are already using Teams

Any