If a mailbox (A) has been configured with another mailbox (B) with Send on Behalf permissions and I want to give mailbox (C) Send on Behalf permissions to (A) also, if I run Set-Mailbox MailboxA -SendOnBehalfTo MailboxC what happens is Mailbox (C) is given this permission and mailbox (B) has it's permissions removed. Can you tell me how to add Mailbox (C) without removing Mailbox (B)'s permissions

$a = (get-mailbox <name>).GrantSendOnBehalfTo $a += <new-mailbox-user.distinguishedname> set-mailbox <name> -GrantSendOnBehalfTo $a That's one way of doing it.--- Rich Matheisen MCSE+I, Exchange MVP