Yes. This is exactly what Xeams is going to do in Hybrid mode - it will filter junk, forward good messages to the server downstream and will hold a copy locally that can be used by either POP3 or IMAP.

However, if you already have an IMAP server down stream, running Xeams in Hybrid mode will duplicate every user's mailbox on two machines. If you don't care about extra disk usage, this is fine. If you don't want to duplicate messages, run Xeams in Firewall mode and put another instance of Xeams downstream that takes care of these IMAP users.