Exchange 2010 | Error trying to add senders to “accept messages from”

When in the Exchange Management Console (EMC), you try to add more users to an existing list under:
mail flow settings>message delivery restrictions>Accept messages from>Only senders in the following list

… you receive an error ‘Couldn’t find object “juser”‘, and the process fails. You have no means to add users. The problem stems from a disabled user object in the current list.

Here’s a low-tech, Exchange Management Shell process to resolve the issue.

Step 1 –
Run the series of commands shown below (as you may know, the ‘-id room222’ identifies the mailbox you wish to modify):

$kab = get-Mailbox -id room222
$kab2 = $kab.AcceptMessagesOnlyFrom | get-user
$kab2 | ft samaccountname

Step 2 –
The last of the above commands produces a samaccountname list of those the mailbox is currently configured to accept messages from; select and copy that list to the clipboard and paste into a text editor. Edit them into a one-line list separated by commas, then paste as the values for the final parameter of the command show below:

set-Mailbox -id room222 -AcceptMessagesOnlyFrom jdoe,adoe,bdoe,cdoe,ddoe,juser

Step 3 –
When you run the above command, the problem user object will produce the error: Couldn’t find object “juser”. Use the up arrow to repeat the command, but edit out the problem user before again running the command:

set-Mailbox -id room222 -AcceptMessagesOnlyFrom jdoe,adoe,bdoe,cdoe,ddoe

Step 4 –
When the command runs without error, you have eliminated the problem users. Now repeat the command again, but add the samaccountnames of any new users to the end of the comma-separated list.

That’s it. NOTE that this command does not append to the existing user list; every time you run it, you completely replace the prior AcceptMessagesOnlyFrom list. That is why you need the complete comma-separated list when you run the command.