We have a requirement to remove users from the "Accept messages from" and reset it to All senders using powershell scripts. To add a user I use -AcceptMessagesOnlyFrom from the set-mailbox cmdlet. I can't seem to find to cmdlet to remove a user from the Accept Messages from area of the Message Delivery Restrictions for a nominated user. Any assistance appreciated. - Wayne

-AcceptMessagesOnlyFrom $null

Thanks Andy, We have since found that $default also works