Background:
I have had a linux server running for about a year now. I have seven user accounts. I and am using postfix as the MTA and apache and horde as the front end for webmail, as well as pop and smtp servers.

All of the users of the server have regular linux accounts even though they are never at my site and there is no telnet or ssh access. There is one exception to this as one other super user logs in through ssh in order to do remote backups.

I am using linux accounts because I allow file access (though horde) which is done with ftp to localhost (ftp is not allowed through the firewall - only localhost)

Questions:
1) Are linux accounts the proper and best type of account for giving people mail accounts (and allow them to access files through horde)?

2) I am currently using FC1 and would like to move to a different distribution. How can I move the users and their archived mail with little or no interruption?

Thanks!