Drafts For Mac
Does he have Outlook opened on another machine? Or do you have something that files email or monitors the sent items folder? I have seen this happen in the past with EWS clients and the Email Filing portion of older versions of iManage's Filesite. So if you have something similar that could be the cause.
Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread. He could have Outlook running in his Terminal Server Session. Could this be a problem? When he sends an email from Outlook Mac we go to the TS and see the email laying as a draft in Sent Folder.
Only from the Windows client we can press 'Send' as the email appears to be sent on the Mac. What Add-ins are running on the terminal server?
Drafts App For Mac
Can you run Outlook in safe mode on the terminal server and see fi you can reproduce it? Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.