This is caused by VERY large (> 10Mb) single part mime encoded message with a Content-Disposition type of "inline".
The problem is introduced by the Content-Disposition type of "inline" which is intended to inform the reading mail client to carry out some operation on the message, in this case to unzip the attachment. GMS Webmail does not support these operations and so was getting confused.
Build 3032 overcomes this issue by treating the attachment as a normal attachment rather than an inline one.
Keywords:WWW 100% CPU single part mime message www.exe