converting password hashes

[Wojciech Puchar]

i want to convert accouts from one system where there was mail-only 
accounts using dovecot/postfix based system and SQL tables to my system, 
where accounts are real unix accounts - that do mail and other things.

I don't know all people's plaintext passwords, and i don't need to and 
want to, but i want new accounts to work with the same passwords

in SQL tables there are entries like this:

$1$aab7638c$Cn7BA/oU4mzr0QltXzV7Z0

and these works by simple cut and paste to /etc/master.passwd file


but there are entries like:

{PLAIN-MD5}c575f55800a549930b9063b43af04f47

that doesn't


is there a way to make it work without contacting over hundred people and 
telling them what new password they have?