cannot send email notification to different domain

[bahaa_issa83]

hi everybody, when any user from out domain try to register for mantis the account is created but they cannot get the email notification.
for examply my domain email is name@engineer.com, if any body try to register with yahoo or hotmail or any other emails they cannot get email notification.
i have firewall. how i can configure config_inc.php to get the email?

thanks

[Kirill]

1. On your mailserver mail come or lost too?
2. What are you use for send mail?