telnet: Unable to connect to remote host: Connection timed out

Question

Setting up a postfix server, trying to figure out why it's not working. Here's a command that I ran while troubleshooting. I expected to be able to connect, but could not.

lol@foldingmachine:~$ telnet a.mx.mail.yahoo.com 25
Trying 67.195.168.31...
telnet: Unable to connect to remote host: Connection timed out

Here's some traceroute output:

lol@foldingmachine:~$ sudo traceroute -n -T -p 25 a.mx.mail.yahoo.com
traceroute to a.mx.mail.yahoo.com (67.195.168.31), 30 hops max, 60 byte packets
 1  192.168.1.1  1.040 ms  1.373 ms  1.719 ms
 2  * * *
 3  * * *
 4  * * *
 5  * * *
 6  * * *
 7  * * *
 8  * * *
 9  * * *
10  * * *
11  * * *
12  * * *
13  * * *
14  * * *
15  * * *
16  * * *
17  * * *
18  * * *
19  * * *
20  * * *
21  * * *
22  * * *
23  * * *
24  * * *
25  * * *
26  * * *
27  * * *
28  * * *
29  * * *
30  * * *

I need to read the Traceroute docs, I'm not sure how to interpret this. Going to bed right now, just hoping somebody will take a look and have a suggestion by tomorrow :)

EDIT:

Ran ncat ("netcat" on my system, apparently) like the answer described. Here's my dig output:

dig yahoo.com mx
...
;; ANSWER SECTION:
yahoo.com.              171     IN      MX      1 mta5.am0.yahoodns.net.
yahoo.com.              171     IN      MX      1 mta7.am0.yahoodns.net.
yahoo.com.              171     IN      MX      1 mta6.am0.yahoodns.net.
...

And netcat:

netcat -v mta6.am0.yahoodns.net. 25
netcat: connect to mta6.am0.yahoodns.net. port 25 (tcp) failed: Connection timed out
netcat: connect to mta6.am0.yahoodns.net. port 25 (tcp) failed: Connection timed out
netcat: connect to mta6.am0.yahoodns.net. port 25 (tcp) failed: Connection timed out
netcat: connect to mta6.am0.yahoodns.net. port 25 (tcp) failed: Connection timed out
netcat: connect to mta6.am0.yahoodns.net. port 25 (tcp) failed: Connection timed out
... (it keeps trying)

So even though a.mx.mail.yahoo.com is actually non-existent, I can't reach the real server either.

Compare it to `traceroute -n -T -p 80 wwwl.yahoo.com`. Most likely a firewall blocks outgoing SMTP connections to port 25 as outgoing spam prevention. — AnFi, Nov 10 '17 at 09:29
That gets through just fine. Given the posted traceroute output, is it possible to tell where the firewall is? On my router (192.168.1.1) or behind it? — jcarpenter2, Nov 10 '17 at 09:34

score 1 · Answer 1 · answered Nov 10 '17 at 11:04

Yup, I've got the same result as you.

ncat -v a.mx.mail.yahoo.com 25
Ncat: Version 6.47 ( http://nmap.org/ncat )
Ncat: Connection timed out.

But it doesn't trouble me at all:

dig yahoo.com mx
...
;; ANSWER SECTION:
yahoo.com.              1428    IN      MX      1 mta6.am0.yahoodns.net.
...

ncat -v mta6.am0.yahoodns.net. 25
Ncat: Version 6.47 ( http://nmap.org/ncat )
Ncat: Connected to 74.6.137.64:25.
220 **************************************

Bingo.

telnet: Unable to connect to remote host: Connection timed out

1 Answers1