hi all, I am not sure about this one. I have granted the send as permission to user A who would like to be able to send as user B after adding the mailbox as an additional mailbox to user As account there is a bounce message saying You do not have permission to send to this recipient is there something I am missing? Thanks

The bounce message shows, UserB is not able to send to some email address. Try to send from UserB's mailbox itself (Not send as) to verify thisRegards from ExchangeOnline | Windows Administrator's forums

thank you all this is now resolved

To send as someone else we do not need to add additional mailbox. Just click From and select a user from the drop down list. Fiona Liao TechNet Community Support