How to check if mail ports on leased server are blocked?

Question

I recently switched companies on a dedicated web server and strongly believe that they are blocking ports 25 and 110. Initially, I thought that it was my active Windows Firewall settings but reviewed them and even turned the firewall off.

Next, I checked the open status on a few different online port testing sites and both email ports were reported as closed.

Then I checked other servers IP addresses in my general ip range and email ports were all closed as well. This leads me to believe that they don't want people running email server software.

After contacting my new host, they are acting as if the problem is my fault and that they need me to get on a support maintenance plan in order to look at it.

I ran the netstat test at the link below and there is nothing listed for the pop3 or smtp sockets (xxx.xxx.xxx.xxx:25 or 110).

How to check if a port is blocked on a Windows machine?

Is there a way for me to somehow check if the webhost's gateway is blocking these email ports? Thank you

Are you interested in inbound traffic or outbound traffic? – Michael Hampton Jan 05 '15 at 03:00 — Michael Hampton, Jan 05 '15 at 03:00
@MichaelHampton, I am interested in inbound traffic. – Caroline Beltran Jan 05 '15 at 03:22 — Caroline Beltran, Jan 05 '15 at 03:22
If you have telnet, try the telnet test in the linked post. – Katherine Villyard Jan 05 '15 at 03:27 — Katherine Villyard, Jan 05 '15 at 03:27

score 1 · Accepted Answer · answered Jan 05 '15 at 03:28

By leased server I presume you mean a dedicated server.

It's rather odd for a dedicated server provider to block port 110.
Some may block outgoing traffic to port 25 to avoid getting their IP ranges blacklisted for spam but blocking port 110 doesn't make much sense to me.

If you are referring to incoming traffic I am not aware of any provider that blocks those ports for any reason.

Are you positive that you are running a POP3 service on port 110 and an SMTP service on port 25?

You can check that (if you are runnning linux) with netstat -npa | egrep "\:25|\:110"
On a standard cPanel installation the output of the above command is something like this

root@server [~]# netstat -npa | egrep "\:25|\:110"
tcp        0      0 0.0.0.0:110                 0.0.0.0:*                   LISTEN      29114/dovecot       
tcp        0      0 0.0.0.0:25                  0.0.0.0:*                   LISTEN      29266/exim          
tcp        0      0 :::110                      :::*                        LISTEN      29114/dovecot       
tcp        0      0 :::25                       :::*                        LISTEN      29266/exim

If both an SMTP and and POP3 services are running then you should check the iptables to see if there are any rules blocking ports 110 & 25.

Finally to actually check if the ports are actually open you could run a simple telnet servers_IP_address 25 and a telnet servers_IP_address 110 outside the server's network.

If the ports are actually open you should get an output like this

$ telnet servers_IP_address 25
220-your.host.com ESMTP Exim 4.84 #2 Mon, 05 Jan 2015 05:18:43 +0200
220-We do not authorize the use of this system to transport unsolicited,
220 and/or bulk e-mail.

$ telnet servers_IP_address 110
+OK Dovecot ready.

If you get a timeout and there is no firewall on your server and the services are running properly then probably your provider does block traffic to those ports.

Your telnet and netstat suggestion helped me to figure out that something is wrong with my mail server. What is odd is that the self diagnostics report that everything is fine and the POP3 and SMTP services 'appear' to be ok but just are not listening. I'm glad that I did not defame my hosting company. — Caroline Beltran, Jan 05 '15 at 17:53

How to check if mail ports on leased server are blocked?

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