Creating Shell-less E-Mail Accounts?

Ryan asks: "I work for a small ISP (2000 e-mail clients) and my task is to create a Web interface so that we and our affiliates can enter a username, password, and e-mail address(es) along with any other pertinent information for a client and have them be automatically entered into our radius table and MTA/POP server's tables. Sendmail supports LDAP, however there doesn't seem to be a POP server that also supports it. There is EXIM with its native MySQL support, and a patch for qpopper to work with it, but it has the downside of requiring the POP3 username to be username@hostname.com. Has anyone found a better solution for creating e-mail users using SQL databases rather than physical shell accounts? Qmail appears to do all of this, but I'm not sure if it does it exactly how we need it to. Any suggestions?"