Alright, here's the a snippet of the SMTP related config:
// use this host for sending mails.
// to use SSL connection, set ssl://smtp.host.com
// if left blank, the PHP mail() function is used
// Use %h variable as replacement for user's IMAP hostname
$rcmail_config['smtp_server'] = 'mail.smumn.edu';
// SMTP port (default is 25; 465 for SSL)
$rcmail_config['smtp_port'] = 25;
// 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';
// SMTP AUTH type (DIGEST-MD5, CRAM-MD5, LOGIN, PLAIN or empty to use
// best server supported one)
$rcmail_config['smtp_auth_type'] = '';
// SMTP HELO host
// Hostname to give to the remote server for SMTP 'HELO' or 'EHLO' messages
// Leave this blank and you will get the server variable 'server_name' or
// localhost if that isn't defined.
$rcmail_config['smtp_helo_host'] = 'mail.smumn.edu';
// Log sent messages
$rcmail_config['smtp_log'] = FALSE;
// Log SQL queries to <log_dir>/sql or to syslog
$rcmail_config['sql_debug'] = false;
// Log IMAP conversation to <log_dir>/imap or to syslog
$rcmail_config['imap_debug'] = false;
// Log SMTP conversation to <log_dir>/smtp or to syslog
$rcmail_config['smtp_debug'] = TRUE;
// How many seconds must pass between emails sent by a user
$rcmail_config['sendmail_delay'] = 0;
Also, I know for a fact that only the part before the @ character in the email address is needed to login and authenticate for SMTP. It does not require it and will not work with the full address.