I have a mailbox using activeSync.
If i delete one or multiple emails from outlook for pc or mac (both very latest versions) Then i go to webmail or check email on my iPhone the items still exist and often show unread.
Sometimes I can delete 50+ emails in the morning from my inbox on my computer and they still exist server side.
If i delete them from my iPhone/iPad (also using ActiveSync) then that does successfully remove them from the server, the issue appears to only be with Outlook for both windows/mac.
Running latest stable build of Smartermail Enterprise Edition 15