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

[Stan Hoeppner]

On 8/24/2013 4:20 PM, Sulla wrote:

> 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
...
> 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.

Basic IP networking problem.

Your ISP is using the RFC 1918 class A private address space for its
customers because it apparently has too little routable public space.

Adding insult to injury you have configured the same class A subnet
10.x.x.x on the LAN segment of a consumer DSL "router" which is not an
IP *router* at all.  It is a Network Address Translation device.  You're
telling it to translate 10/8 to 10/8 which is impossible.

The solution?  Simple.  You must use one of the other two RFC 1918
private address spaces on the LAN segment of your NAT'ing DSL modem.
Here are all three.  Pick one that is not 10/8.  Hint, most people use
192.168/16 because the subnet masking is easier to remember, and because
few people have more than 256 devices on their home network.

     10.0.0.0        -   10.255.255.255  (10/8 prefix)
     172.16.0.0      -   172.31.255.255  (172.16/12 prefix)
     192.168.0.0     -   192.168.255.255 (192.168/16 prefix)

-- 
Stan