We have moved from a cloud based IMAP solution to an on premise Exchange 2013 on the 13/04. All users were imported from AD and assigned mailboxes using Powershell. Everything so far has gone well until today when we discovered that any user can send email as any other user even though they don't have permissions to do so!  We've checked that users aren't members of any Exchange groups or admin groups that would allow this and checked through Powershell that the send as permission isn't applied!

We're stumped and we need to get this resolved ASAP.  Any help would be appreciated.

Thanks in advance :-)

• Edited by Slide71 11 hours 26 minutes ago

Then they are the member of a group that has that right.