[Dovecot] dovecot OK for intranet, not OK for external IPs

[Sulla]

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Dear all!

I'm stuck.

I've got a dovecot IMAP server running (TLS, port 149) on Ubuntu 13.04
server behind a DSL router. The mailserver's IP is 10.0.0.1

When I connect to my mailbox from my intranet-PC (10.0.0.2), everything
works as expected. Login OK, acces to all mailboxes is ok, everything.

netstat -nt on my email server shows me:

Proto Recv-Q Send-Q Local Address Foreign Address    State
tcp        0      0 10.0.0.1:143  10.0.0.2:57952     ESTABLISHED

and /var/log/mail.log shows me:
Aug 24 22:41:00 SERVERNAME dovecot: imap-login: Login: user=<UID>,
method=PLAIN, rip=10.0.0.2, lip=10.0.0.1, mpid=24326, TLS,
session=<3Ul+irfkYAAKAAAC>



However, when I connect to my mailserver through the internet (from
10.196.124.7 which is a modem of my ISP), dovecot ignores the
authentication request. It does nothing. Just nothing.

My router forwards the connection request to my mailserver correctly, so
port forwarding on the router is ok, as my mailserver gets a connection
request from the client. Proof: "netstat -nt" shows me:

Proto Recv-Q Send-Q Local Address  Foreign Address     State
tcp        0      0 10.0.0.1:143   10.196.124.7:1024   SYN_RECV

So, my server gets a connection request on port 143 from my client PC, but
then nothing happens. By nothing I mean, that nothing gets written into
/var/log/mail.log and my email client (Thunderbird) gets a connection timeout.

Any ideas why dovecot is refusing connections? How can I solve this problem?

thanx all
Sulla



















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