Using Entourage for Mac (2004 or 2008) while connecting to an Exchange 2007 mailbox on a Windows 2008 Server, user cannot download any e-mail message which has a plus sign in it's subject line, like 'Test + Mail'.
Amir Haque discuss the fix here: E-mail Download Issue in Entourage With Exchange 2007 on Windows 2008

Comments (1)
We have applied the server-side updates discussed in the fix post, but users continue to see issues with a plus sign in the subject. Has there been any further discussion or exploration uncovering other information? We have found that updating Entourage to the 13.x beta does fix our issue.
Thanks,
Michael
[Note: 13x beta refers to the EWS beta for Exchange]