In old PM System, we had ability to forward outside emails (with attachments) to tasks, in order to record them to the activity or project. This was critical for us, because many requestors / guest users will start a message by traditional email, so it can't get recorded as activity to the project without a lot of manual work.
It would be GREAT to have ability to forward an email to the Project ID / Name...the old system used a Subject Line Matching system with the same email address for our account. So the email we sent it to was always the same, but hte Subject Line would change. This was a feature in 5pmWeb, if you are interested in researching it.