Attempting to decommission an Exchange 2003 server throws the error: “The component “Microsoft Exchange Messaging and Collaboration Services” cannot be assigned the action “Remove” because: - One or more users currently use a mailbox store on this server. These users must be moved to a mailbox store on a different server or be mail disabled before uninstalling this server.”

As many Exchange 2003 to 2007 and 2010 migrations I’ve done over the years, I think the part of the migration I dread most is the end of the migration when the Exchange 2003 server needs to be decommissioned.  Other than making sure that all the mailboxes are moved, public folders fully replicated and moved over, and all of your legacy routing connectors are recreated for large organizations that still have Exchange 2003 servers, I find that I almost always receive errors when I try to use the Add and Remove Programs wizard to uninstall Exchange.

Just when I thought I’ve seen all of the possible reasons why an uninstall would fail, one of the recent Exchange 2003 migrations threw me the following new error:

The component “Microsoft Exchange Messaging and Collaboration Services” cannot be assigned the action “Remove” because:
- One or more users currently use a mailbox store on this server. These users must be moved to a mailbox store on a different server or be mail disabled before uninstalling this server.

This was the last error of the 3 I fixed (the other ones being routing members and routing groups) and while I’ve seen something like this before where various users weren’t visible by browsing the mailbox stores on the Exchange 2003 servers via the System Manager console, so you had to use the following KB:

Error message when you try to remove Exchange Server from a mailbox server that no longer hosts mailboxes: "One or more users currently use a mailbox store on this server"
http://support.microsoft.com/kb/924170

To launch Active Directory Users and Computers, use the Find tool to search for users via the Exchange tab while checking:

• Show only Exchange recipients
• Users with Exchange mailbox

Then use the View tab to select the Choose Columns… option:

Then add the column Exchange Mailbox Store:

… then finally use the Exchange Home Server tab to sort the users and locate the mailboxes that are still associated with the Exchange 2003 server you are trying to decommission:

This has always worked for me but not for the last migration because no matter which domain I searched, I could not locate any mailboxes that are associated with the server I was trying to decommission:

After triple checking all the domains, I proceeded back to Google to see if I could find something that would help and that was when I came across this post:

http://social.technet.microsoft.com/Forums/exchange/en-US/2758744e-ab92-45af-bc01-5a1280887230/one-or-more-users-currently-use-a-mailbox-store-on-this-server?forum=exchange2010

So apparently there was another way to try searching for these mailboxes and that is to select the Custom Search option in the Find drop down menu:

Select the Advanced tab:

In the Enter LDAP query textbox, type in:

objectClass=User

Searching with this method finally revealed the mailboxes I was looking for:

Proceeding to select the accounts with the mailboxes and then using Exchange Tasks… enabled me to remove these mailboxes and proceed with the uninstall:

Once the mailboxes in question have been removed, proceed with restarting the uninstaller and the error should go away: