I have an Exchange 2010 server, running on Windows 2008 R2. To make an email sending program work in one of my internal applications, I created an account, and then set Send-As permissions for that account on about 15 user mailboxes. This worked fine for a while, but then the Send-As permission for that account goes away on those mailboxes after some period of time and breaks the program. This error is returned:
"The server response was 550 5.7.1 Client does not have permissions to send as this sender"
If I set the permission again, it will work for a while and then disappear from the accounts. I am doing this through the management console, by going to Recipient Configuration\Mailbox
Right-click the user and choose Manage Send-As permissions. Then I click Add and choose the new account I created and click the Manage button to apply the change.
I am not an Exchange expert by any measure, so any help would be greatly appreciated.