Don't flame me, but i don't think it's possible to
inject
a .pst file into Qmail. Qmail uses the mbox or maildir format for storing mail.
See section 4 in
http://www.lifewithqmail.org/lwq.pdf Microsoft .pst file format is propriatary to Microsoft and doesn't sync well with other mail systems.
Your only option is to create the users on the SME Server and have it respond to your incomming mail. Then with your existing mail clients (Assuming outlook) connect to the mail server as you normally do with Exchange and donwload all the messages.
The only reason your receiving the suggestion about imap is with the imap system, the mail is retained on the server. Makes it much easier to backup and restore.
Microsoft exchange uses a similar method to the imap protocol. When you utilize the exhange system, the messages still reside on the mail server.
Does this help, but don't flame me,
Darin MacLachlan