I don't know in the last statement whether it is reffered are not, this link mailbox may come if you had disabled mailbox also
We then setup Exchange 2007 running alongside the 2003 server. Migrating users who were part of our COMPANYHQ domain caused no issues. They all worked perfectly. The migrated users on the MINISITE domain however didn't work. They could open and view their mailboxes - however they said they did not have permission to send.
Now here is my mistake - remembering the 2003 migration I quickly went off to find out how to grant these permissions to the account again - except this time it made no difference. It still did not work. Not matter what the remote site always claimed it didn't have permission.
The key was the type of mailbox it is - it needs to be a "Linked Mailbox". Upon migrating all my MINISITE users were coming across as "Shared Mailboxes".
Now this probably isn't the only way to do this - I imagine you can do this with the PowerShell but here is what we did to correct the issue (remember this will probably ONLY occur if you migrated from 5.5 to 2003 (and hence put in the SELF account in as "Associated External Account")).
1) Migrate all MINISITE mailboxes (so the COMPANYHQ\userA mailbox which MINISITE\userA will access) back on to the old 2003 server
2) Using active directory go to the user.
3) Under "Exchange Advanced" go to "Mailbox Rights"
4) Delete the "SELF" account (or if you are worried about it being there, remove its "Associated external account" permission)
5) Select the MINISITE\userA user and assign them "Associated External Account" (and we gave "Full Mailbox Access" as well)
6) Re-Migrate the mailbox back on to the Exchange 2007 server
7) Check that the Exchange Manager shows the mailbox type as "Linked Mailbox".
The account should then work as when it was on the 2003 server.
The above information took from this blog
If you feel still i am unclear then please explain it in much detail