Using Gmail whenever you send emails back and forth and it has the same subject title, it keeps it in 1 email separating each response instead of cluttering your inbox with a bunch of emails with the same subject title.

I was wondering if we can do something like that with our PMs since we only have a 50 message limit.

No, it can't really be done without underlying changes to the database structure, which I don't have time to do, as it would be a HUGE project.