That's a work process thing that I don't think I would tackle in Project.
Instead, setup a email receiving system that matches your work processes
to distribute incoming emails into relevant folders. To get the
incoming mail into the right folders, perhaps easiest way is to setup
specific email address for each project. Give individuals access to
relevant email folders via their email client software. Depending on
how automated you want this to be, you could explore doing some
filtering on the incoming email on the mail server to deposit the mail
into special folders, e.g. "for action", "for info", etc. based on the
content of the email, the "from" field, header info, or whatever
distinguishes the mail.
Hope this is useful to you. Let us know.
rms