Change mailbox alias or re-create Exchange mailboxes results in NDR from bad Outlook recipient cache

In the past when renaming or re-creating mailboxes in Exchange I’ve had issues where the Outlook cached entry for the user no longer works when internal users send mail to the specified mailbox. This is because of our dual Exchange environment running mixed versions of Exchange. The original mailbox was created under Exchange 2003 and ultimately moved to Exchange 2007, but preserving the Exchange 2003 Mailbox reference for X500. When a mailbox is re-created or the alias is changed, it can break these cached entries in Outlook. Today, I discovered a way to work around this issue from this article.

In the future if I need to change alias (due to name change) or if there are problems resulting in a need to re-create the mailbox, the steps in the article can be used to avoid having mail delivery problems for the affected user.

• The listed steps will allow the cached Outlook entries to properly resolve the user mailbox. No user action is required to make this work.
• You can find the proper alias for the user in an NDR message or by going to the cached entry in outlook and viewing its properties. It will be a string in one of the values displayed on the properties. (Note, this only works before you make the changes above).
• The updated string for the Exchange 2007 environment is automatically added to re-created mailboxes in X400 form. The old pointers can be added using X500.
• This issue only affects mail sent from internal clients using the cached entry in Outlook, all SMTP mail flow and external mail will continue to flow to the user uninterrupted regardless of this issue.