Hi Marek,
Based on the result of "get-recipient", user1@domain.com is a user mailbox. It has two proxy addresses. One is usr3@domain2.com and the other is usr4@domain2.onmicrosoft.com. What do you mean by saying "Apparently this user is in Office 365...."? Do you mean you can see the user in Office 365, but cannot find it in the local AD? Please clarify it. Moreover, could you translate the Dirsync mail from Swedish to English?
Thanks,
Edward Qu