Why is my IMAP port not showing as open ( yet it works? )

Question

Ive recently setup Postfix and Dovecot IMAP on a Debian Lenny box. Sending to this domain works fine and reading the email via IMAP works fine too. I'm curious though as to why when running nmap, port 10143 is not shown as open.

nmap -sS -O 127.0.0.1

Starting Nmap 4.62 ( http://nmap.org ) at 2011-11-26 21:30 GMT
Interesting ports on localhost.localdomain (127.0.0.1):
Not shown: 1711 closed ports
PORT     STATE SERVICE
22/tcp   open  ssh
25/tcp   open  smtp
80/tcp   open  http
3306/tcp open  mysql

Am I missing something with NMAP?

Thanks

Leo

Answer 1

run the following

netstat -tlupn | grep 143

Maybe imap isn't set to be bound to 127.0.0.1?

Answer 2

man nmap

nmap doesn't scan all ports by default. (it would be a lot slower if it did.)

Instead "By default, Nmap scans the most common 1,000 ports for each protocol."

You're running IMAP on a non-standard port, and nmap isn't looking there.

You can tweak nmap to scan different port ranges if you'd like.

-p 10100-10200