Notes users are migrated to Exchange and their mail forwarding is being set as part of the migration [Manage Mail Routing]. However when Notes users are sending these users email, the messages are being delivered into their Notes Mailboxes.
Domain: Single name space
Domino 8.5.1 FP3
The forwarding addresses were appended with a Domino Domain name. In some instances this was causing the Domino router to deliver the mail locally to a Notes mail box rather than to Exchange.
This issue as resolved by removing the appended Domino Domain. Once this was done mail started routing immediately.