[SOLVED] Can't connect Thunderbird with my smtp server

[srj]

Hello,

Please inform me if I'm missing something cause I'm lost after one day of searching google and other sources.

I have a smtp server behind a NAT router that's working fine (with the help of my ISP's relayhost smtp server).
Dovecot is running on the same machine using the IMAP protocol.
I can send/receive mails from the server without issue and dovecot is running listening on all addresses.

Problem:

When I'm trying to connect Thunderbird using the external domain name (example.com port 143) it "can't find the settings on my e-mail account".

The dovecot server is running with minimal settings (plain text password connections)

If I configure Thunderbird to use the server's internal address (private IP address) from inside the network everything is working without issue. (I can send receive mails).

Now, you might say I have something blocked from the outside.
That can't be true because I tried from another network and I could successfully connect to dovecot using telnet example.com 143 but again, can't do it using Thunderbird.

From the telnet session I could connect, authentificate and fetch mail items.

Ports 25, 143, 110 and 53 are all forwared to my internal server's IP address and are open from outside.

Is Thunderbird trying to connect using port numbers other than 143 and 25? Perhaps I need to forward a couple of more port numbers if so.

Thank you very much for your time in reading my post.

[srj]

I ran using a laptop from my network (Windows machine):

telnet "Internal IP" 143 - Worked OK
telnet "External IP" 143 - Connection failed
telnet "Domain Name" 143 - Connection failed

"http://www.canyouseeme.org/" can see the port 143 open on my "External IP" address.

I'm really lost here

[cnamejj]

I ran using a laptop from my network (Windows machine):

telnet "Internal IP" 143 - Worked OK
telnet "External IP" 143 - Connection failed
telnet "Domain Name" 143 - Connection failed

"http://www.canyouseeme.org/" can see the port 143 open on my "External IP" address.

I'm really lost here

I can't offer much help here, but I do see a possible connection between your situation and another one posted here in the last week or so. It sounds like (with the second post) that you can't connect to the external IP address of the SMTP server from a client on that network. If so, then someone posted a similar questions recently. The response receive was to make sure the device providing the NAT service will handle that flow. It might not be setup to broker as NAT-IP1 -> Ext-IP -> NAT-IP2 connection.

[srj]

Hello cnamejj,

Thank you for your reply. It was indeed the same issue as you mentioned.
To be more specific I think my ISP is blocking outgoing ports 25, 143, 110, 80 and more, which caused me a 2 days headache.

When I found the ports open from the "Internet" I never thought they'd be blocked the other way around.
Perhaps Thunderbird managed to connect using the default port but the server was unable to respond back because the same port number was blocked in it's way.

I'm not 100% sure it's true and I don't have any servers outside to test it but after I changed the default ports to some random ones everything worked out fine.

Thank you very much for your support as always,
Sergiu