I set up my mail server on OS X 10.4 and enabled SquirrelMail to provide webmail functionality. In my Mail Preferences for authentication, I had disabled LOGIN and PLAIN, so passwords wouldn't be sent in the clear when people check their mail. With these settings, I could not login to my webmail. Using the conf.pl script in the squirrelmail directory, I could not change the authentication method, so I had to change it manually like this:
Open Terminal and type pico /etc/squirrelmail/config/config.php. Change $imap_auth_mech = 'login'; to $imap_auth_mech = 'cram-md5'; (or whatever you set as your method for authentication). Save and close the document. Now you can login to SquirrelMail using your username and password....

