squirrelmail does not send mail out in fc3?

Hi,

I have a problem with squirrelmail in fc3.  I installed it
(squirrelmail-1.4.3a-6.FC3) from the fc3 cd. I can receive and read mails
in squirrelmail.  However, I cannot send mails out, no error, but nothing
happens when I click Send.

My dovecot.conf sets

protocols = imap imaps pop3 pop3s

and I can read/send mails from outlook express without error, dovecot is
running.  I also tried to set in /etc/squirrelmail/config.php

$domain                 = 'localhost';
$imapServerAddress      = 'localhost';
$smtpServerAddress      = 'localhost';

and

$domain                 = 'my-server-name';
$imapServerAddress      = 'my-server-name';
$smtpServerAddress      = 'my-server-name';

but, none of them works.  The firewall is turned off.  I used the same way
to set up squirrelmail in fc1 and it is working well there.  Should I do
something else in fc3 to make it working?

I appreciate all help!

Hongwei Li