You import a PST file to a Microsoft Exchange Server 2013 mailbox by running the New-MailboxImportRequest Windows PowerShell cmdlet.
You open the mailbox in Microsoft Outlook, and then you try to reply to an email message that was imported from the PST file.
In this scenario, the display name of the sender of the original email is in the To field. However, the display name does not contain the SMTP address.
This issue occurs because the Exchange store does not add a certain property automatically when email messages are copied from a PST file. Therefore, Outlook cannot import recipients' information correctly.
To resolve this issue, install the following update:
2936880 Cumulative Update 5 for Exchange Server 2013
To work around this issue, reply to the email message by using Outlook Web App.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
For more information about the New-MailboxImportRequest cmdlet, go to the following Microsoft website: