How to use old md5 password hashes on courier/postfix

I've recently installed courier/postfix with virtual users and domains and i want to move mailboxes from an old server. The problem is that the old server used to use md5 password hashes in the database and current server uses mysql's encrypt(). I've tried to use the following things in the password field with no luck:

{PLAIN-MD5}old_hash
{MD5}old_hash
 $1$old_hash

Courier does not allow me to login. Where could i change a setting or something to allow both courier and postfix to understand old password hashes?