Ive done this before...
But I remember pulling my hair out for an afternoon to get it set up for one user.
If we have one mailserver and one Exchange organisation with a domain xyz.com
I want to add 123.com (Yes I know I can add it to the default recipient policy)
What I want is
firstname.lastname@example.org to send and receive as email@example.com
and Joe.firstname.lastname@example.org to send and receive as email@example.com
Before I HAD TO create two users called joe.bloggs (in different OU's) create two mailbox's give one access to the others mailbox, and set up two outlook profiles on joe.bloggs PC, I also remember I had to do everything in a specific order to avoid having two joe bloggs on the GAL and be able to connect to both mailbox's, and I had to untick "Update Email from default recipient policy" on the user objects.
So How Did I do it before? Is there a better way of doing it?