I need a bulk (checkbox) way to clean up mail erroneously associated with particular deals.  Doing this in the deal means multiple clicks for every message.   However, if there were a way to filter by messages associated with specific deals in Mail, this would allow you to Select All or quickly check specific messages and delete them.  

p.s.  This mess is caused primarily by Subject line based thready, which I know you mean to be a feature, but it makes a mess when you send a bunch of messages out to different prospects with the same subject line.