Issue Definition: 451 4.4.62 Mail sent to the wrong Office 365 region. ATTR35. Issue Resolution: As per our investigation done, Kindly be informed that the recipient is in a different region than where the message landed. This could be because the sender is smart hosting and intending to relay through their tenant first but their inbound connector configuration is not working as intended. nullnullnullnullnullnullnullnullnull
Configure a certificate-based connector to relay email messages through Office 365, Office 365 Message Attribution - Microsoft Tech Community
In case of any queries or concerns or if the issue reoccurs, you can reopen this case within 7 days through Office 365 admin portal (https://portal.office.com).