I have a user that is booking a meeting with 5 people. Two are local on our Exchange server and 3 are outside the company. He claims they are valid email addresses and he sends email to them. He gets the error message below immediately back for each user.
This message could not be sent. Try sending the message again later, or contact your network administrator. Error is [0x80070057-00000000-00000000].
Its listed 5 times. One for each user.
I don't even know where to start. He claims this has worked before.