Can't Telnet to remote host - but can telnet locally (Ports 110,143,993,995)

Question

I've been attempting to set up a Mail Server Via PostFix and DoveCot on ubuntu 14.04 for too long now and I'm on the home stretch of having it working.

I'm running a virtual machine with ubuntu, I have port forwarding set up to my virtual machine on all ports for imap/pop (110,143,993,995).

If I do the 'telent localhost ' on any of the ports listed above I am able to connect

root@ubuntu:/# telnet localhost 110
Trying ::1...
Connected to localhost.
Escape character is '^]'.
+OK Dovecot (Ubuntu) ready.

root@ubuntu:/# telnet localhost 143
Trying ::1...
Connected to localhost.
Escape character is '^]'.
* OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE     STARTTLS AUTH=PLAIN AUTH=LOGIN] Dovecot (Ubuntu) ready. 
a1 login < username > < password >
a1 OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS THREAD=ORDEREDSUBJECT MULTIAPPEND URL-PARTIAL CATENATE UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS SPECIAL-USE BINARY MOVE] Logged in

root@ubuntu:/# telnet localhost 993
Trying ::1...
Connected to localhost.
Escape character is '^]'.

root@ubuntu:/# telnet localhost 995
Trying ::1...
Connected to localhost.
Escape character is '^]'.

as soon as I try to do them via the public Ip it fails:

root@ubuntu:/# telnet < my domain > 110
Trying < ip of my computer that has port forwarding to my vm >...
telnet: Unable to connect to remote host: Connection refused

If I do a 'netstat' to figure out what's going on at what ports you can tell I'm listening on the correct ports

root@ubuntu:/# netstat -nl4
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State   
tcp        0      0 0.0.0.0:25              0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:9306            0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:15674           0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:47580           0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:445             0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:9312            0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:993             0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:995             0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:3306            0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:587             0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:139             0.0.0.0:*               LISTEN     
tcp        0      0 127.0.0.1:61613         0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:110             0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:143             0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:465             0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:21              0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN     
tcp        0      0 0.0.0.0:15670           0.0.0.0:*               LISTEN 

#...
#... theres a few more ip's in here that I believe to be irrelevant

and lastly just to be sure it is dovecot that is listening there ...

root@ubuntu:/# netstat -antup|grep dovecot
tcp        0      0 0.0.0.0:993             0.0.0.0:*               LISTEN      104305/dovecot  
tcp        0      0 0.0.0.0:995             0.0.0.0:*               LISTEN      104305/dovecot  
tcp        0      0 0.0.0.0:110             0.0.0.0:*               LISTEN      104305/dovecot  
tcp        0      0 0.0.0.0:143             0.0.0.0:*               LISTEN      104305/dovecot  
tcp6       0      0 :::993                  :::*                    LISTEN      104305/dovecot  
tcp6       0      0 :::995                  :::*                    LISTEN      104305/dovecot  
tcp6       0      0 :::110                  :::*                    LISTEN      104305/dovecot  
tcp6       0      0 :::143                  :::*                    LISTEN      104305/dovecot 

Port Forwarding has been enabled on all the previously mentioned ports - my firewall is completely disabled and I'm trying to telnet to my own machine so the common error of "The computer you are trying to telnet doesn't have telnet installed" shouldn't apply to me. And if it did - my macintosh has telnet installed as well - so it really does not apply to me.

At this point I'm under the impression that there is a configuration in my router that is blocking me from reaching my computer via the Public Ip.

Any help or insight is greatly appreciated. This is my first mail server install so my knowledge in this area isn't heroic.

Answer 1

You're being stopped by the lack of NAT loopback. You might be able to enable it on your router.