how to send messages on behalf of another user by default?

Hi,

There is no direct way to do this in Outlook, but you can still do some more steps as a workaround.

When you want to change the default to another mailbox to which you also have Full Access permissions, you can configure your mail profile with that mailbox instead and add your own as a delegate mailbox.

The result would be basically the reverse of what you have now; Your own mailbox configured as the Exchange account and the other mailbox added as an opened additional mailbox.

Ask your Exchange administrator if you dont know whether you have been granted Full Access permissions on the other mailbox.

Regards,

Melon Chen
TechNet Community Su