1
I am trying to troubleshoot a connection problem with Thunderbird on a freshly installed Windows 7 computer. For this I have installed telnet and tried to connect to the server through it.
First, I tried SMTP:
computer1> telnet server.example.local 25
220 s6 ESMTP Postfix (Ubuntu)
This worked fine, the server responded as expected, so smtp connections seem to be OK.
Next I tried POP3:
computer1> telnet server.example.local 110
and nothing ever happens. The window remained blank.
If I try the same from different computers (Windows XP, Windows 7 and Windows 8), I get the expected response:
other computers> telnet server.example.local 110
+OK Dovecot ready.
So the server works fine but the connection from the client computer in question apparently gets blocked.
The same with IMAP: On this particular computer:
computer1> telnet server.example.local 143
and nothing happens.
On different computers the same call gets the expected response:
other computers> telnet server.example.local 143
* OK Waiting for authentication process to respond..
* OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE STARTTLS AUTH=PLAIN] Dovecot ready.
Again, the server works fine but the connection from the client computer in question apparently gets blocked.
The server is a local server and all computers are in the same IP subnet. And since SMTP works, I can't see any reason why POP3 and IMAP shouldn't, but they don't.
On the server side, nothing ever shows up in /var/log/mail.log for the connections that fail.
What can block these connections? The Windows firewall? If yes, where should I look? I tried to disable the firewall completely but it didn't seem to make any difference.
dummzeuch
Posted 2014-01-30T11:30:58.550
Reputation: 464
What was your problem again? telnet connections to those services look perfectly normal to me. – PsychoData – 2014-01-30T13:06:57.963
the problem was, that the connections for pop3 and imap did not work at all on that particular machine. The examples on how it should look are from different computers (as I already said in the question, I think.) – dummzeuch – 2014-01-30T13:08:40.663
If your question is literally just what can block SMTP, Pop3, and IMAP connections, then its a long list. Firewall on sending or receiving computer, ACLs in between, Software listening on wrong port, client trying to connect on wrong port, pointed at the wrong server, bad username password (services can be configured to not respond telling you that its bad) and I'm sure there are more I'm missing – PsychoData – 2014-01-30T13:10:01.460
Right, but you're listing three different services. Comparing SMTP on the not working Win 7 box to IMAP and Pop3 on the working machines. Apples and oranges – PsychoData – 2014-01-30T13:12:35.940
I suggest reading the question again. – dummzeuch – 2014-01-30T13:20:56.270
Yes, though it's still tough to read. – PsychoData – 2014-01-30T13:34:29.460