Courier and encrypted passwords

[counterpoint]

My mail server is built largely using "how to" information here, and it is providing POP3 mail serving via Courier. User data is in MySQL and I'm using ViMbAdmin to manage the MySQL data. This works fine for plain text passwords.

But if I change the passwords to being encrypted (ViMbAdmin uses MD5) then the password is rejected. With diagnostics turned up, there is a message in the log, which simply quotes the plain text password submitted by the mail client, and says it does not match the encrypted password (which it quotes) extracted from the database.

The Courier configuration file giving the MySQL information is being modified to contain a reference to encrypted passwords at the same time as the field in the database was changed to encrypted.

Is the wrong encryption being used? Or does Courier need some further configuration?