Ive successfully migrated all mailboxes from Exchange 2003 to new Exchange 2013 server using Code Two. However after migration I found one strange issue for all users and just wander if you could help me.

Basically when user reply to e-mail (only old as new are correctly recognized) using outlook, sender address is not recognized. Only name comes in "To.." filed and is not underlined nor e-mail address is not showed on right site (but I can see it in original e-mail in way CodeTwo Customer Service [mailto:support@codetwo.com] like below). When I click "Send" and the name is not in address book, users get error:

"Microsoft Outlook does not recognize "John Smith" and e-mail is not send". This issue doesnt exist in OWA.

As there is no problem for new incoming e-mails only for migrated, I believe the problem is somewhere in migrated data.

Could you advise please? Have you ever met problem like that?

Did you do a cross-forest migration?

It appears that the legacyExchangeDN attribute of 2003 mailbox was not migrated to the 2013 mailbox.

Hi Zhen,

That is correct. We have done cross forest migration. But we have migrated legacyExchangeDN attribute of 2003 to 2013 as X500.

I am sure this issue doesn't occur when Out look is in Online Mode.
What version of Outlook you are using?