SurgeMail has its own high performance user database system built in but can easily be configured to use existing user authentication databases, or you can configure SurgeMail to access your old POP3 server and then auto create accounts locally.
Other authent modules supported include:
In fact using the new MultiAuth module you could configure SurgeMail to authenticate against any number of these combined. Although this is not the suggested way of doing it as it makes the central management of accounts more difficult - we recommend picking one!.
See the manual and download a module
SurgeMail can be configured to give access to certain mail services (WebMail, POP3 server, IMAP server, or SMTP server) on a per account basis. This could for example limit certain accounts to WebMail only, or allow you to charge a premium for POP access to accounts.