I have setup an email server by following howtoforge guide "http://www.howtoforge.com/perfect-server-ubuntu-12.04-lts-apache2-bind-dovecot-ispconfig-3". Mail server is working perfectly. But the problem is that when someone telnet through port 25 he can send email to internal users without authentication.
I have setup mail server on domain webmail.biz. anyone can connect to that domain via telnet on port 25 and send mails to email id's on same domain like from firstname.lastname@example.org
. I want to stop this anonymous mail sent through telnet. if i close port 25 i don't receive any mail.
Any way to solve this problem.
I need help of this forum urgently