hi leandro
you may have already found this out but you can set a default domain in the main.inc.php file
find this section
// This domain will be used to form e-mail addresses of new users
// Specify an array with 'host' => 'domain' values to support multiple hosts
$rcmail_config['mail_domain'] = ' ';
and modify it as in your example
$rcmail_config['mail_domain'] = 'account.com';
That should work ok provided that your users have email addresses that contain their user name so a user with a login username of bobjones should have an email address or alias of
bobjones@account.com.
hope this helps, I had a similar issue with my install till i saw this parameter.
I expect this is also covered in the support forums as well.
cheers
Neil