BobK_BN

I resolved this. In fact, it has something to do with the address lists, but nothing one could have expected: We're using Outlook 2010. When Outlook wants to send a message one has SendAs rights onto, it does not simply give the address to the mailbox server in question, which would be sufficient, but instead it seems to pass a pointer to the entry in the address list the entry derives from. Having Outlook configured in the way that it starts searching in a customized address list and NOT letting it continue the search in the global address list makes it merely impossible to use addresses from the global address list as SendAs addresses. You have to put those addresses in the customized address list. This is complete nonsense, because Outlook could have let the mailbox server decide wether to accept the message or not (which in fact it does in cached mode!), but I guess we have to live with it. Bob

Yes, it does work each time. But whats notable: The address in question is disappearing from the From: Button, so I have to re-enter it each time I compose a new message. With other accounts, from which the users can SendAs as wanted, the SendAs-addresses do NOT disappear. None of the above change the behaviour: The first email gets send correctly, the following don't. Remarkably, when I delete and re-add the permission over and over, sending emails using the SendAs right at some point works ok. This is not reproducable - sometimes it takes 3 tries, sometimes 6, some work from the very start. Not the game I can play with my users. Remarkable might be, that the SendAs addresses in question are in fact contacts, not mailboxes. SendAs on mailboxes works all the time for every user. If it wouldn't, we'd be at a loss, because none of my users actually use the account they're logged in with to send emails, but use a second mailbox the have FullAccess to and the SendAs right for. It's just some contacts that can't be used as SendAs. We used to set the SendAs right via Add-ADPermission, which after applying SP3 RU2 is not usable anymore. Trying Add-ADPermission throws an Error 5, "Permission denied", no matter which admin tries to use it. Even Exchange Organization Admins cannot set the SendAs right via Add-ADPermission, so we have to use the security tab in ADUC. I don't know if this has something to do with the problem of being unable to actually *use* the SendAs right, but it sounds strange that we cannot set it for contacts and not use it with contacts, so there might be a connection between the two errors. Any hint would be greatly appreaciated.

Does anyone have a solution for the original problem? I'm having the exact same situation - some of my users cannot use SendAs while others can. SendOnBehalfOf is no option in our environment. The problems started after applying SP3 RU2 to all of our EX2010. We have over 60 DCs, some 24 EX with CAS/HUB/MBX roles and 1 DAG, 8 MBX only in 2 stretched DAGs, 6 CAS/HUB only behind LoadBalancers. Removing the address we want to send as and re-adding works for just one email, as described by the others having this problem, but this is not really an option, for sure. If someone has a hint where to look for, I'd be glad. Bob