There are no problem with all things in my links, except email won't send out after validation or modification.
This is my setting...(i host my site in fiberia)

# PATH of sendmail.
$db_mail_path = "/usr/sbin/sendmail";

# Email Notifications
# --------------------------------------------------------
# NOTE: Be sure to edit the text of the message. It can be found
# in the subroutines html_email_add and html_email_modify in
# admin_html.pl.

# Email address of the administrator. BE SURE TO SET!
$db_admin_email = 'mp3searcher@softhome.net';

# Notify visitors automatically when their links are validated?
$db_email_add = 1;

There is also a problem that when i verify the links. The broken link was never shown. It only check the right link but dont have any description with the broken link, even there is realy a broken link...

# Notify visitors automatically when their links are modified?
$db_email_modify = 1;

I believe the "-t" flag needs to be with your path to sendmail. Change it to:

# PATH of sendmail.
$db_mail_path = "/usr/sbin/sendmail -t";

If that doesn't work, you might be pointing to the wrong location for sendmail. See if adding the "-t" works before trying a different location for sendmail.