hi
You should check your config file from your webmail
This is in rouncubed
/ / SMTP username (if required) if you use% u as the username Roundcube
/ / Will use the current username for login
$ rcmail_config ['smtp_user'] = '% u';
/ / SMTP password (if required) if you use% p as the password Roundcube
/ / Will use the current user's password for login
$ rcmail_config ['smtp_pass'] = '% p';
in your webmail you have to look
maybe this helped you
http://squirrelmail.org/wiki/MailServerIMAPProblem
michael