IMAP, POP3 and NNTP functions - questions..

I have a question or two regarding the IMAP, POP3 and NNTP functions. Is there *any* way to use imap_fetchstructure() using an actually message string instead of an imap_stream and messgae number. Basicly, I am storing mail onto a MySQL DB. I want to be able to parse out the attatchments and data. However, I cannot use these functions because it wants a mailbox and not an actual peice of mail. All I really need to be able to do is extract the data (dont need filename, mimetype, etc) into a string, and i can use a base64 decode func to give me the raw data. If anyone has suggestions or solutions, it would be greatly appreciated. Thanks, -topside