[Users] Claws Mail Can't Connect to Internet With Specific Internet Connection

[Paul Rolland]

Hello,

On Tue, 11 Oct 2022 19:38:18 +0600
Dustin Miller <dustbiz at gmail.com> wrote:

> In any case, I am wondering whether anyone (probably a developer) can
> give me a basic idea of what is supposed to happen (i.e.
> 'behind-the-scenes') in the interaction between CM and its host system
> (Linux-based) when a person directs CM to check email? Or perhaps point
> me to a resource or documentation where I could find this out myself?
> Might be a long shot, but I thought I'd check in here to see if I can
> get some info that will help me know how to move forward with
> trouble-shooting this.

POP3: tcp connection to remote port 110 is established, and then dialog
      between CM and the remote server
      183 [15:43] rol at riri:~> telnet riri.xxx.xxx 110
      Trying 10.11.12.13...
      Connected to riri.as2917.net.
      Escape character is '^]'.
      +OK ready  

IMAP4: same, with tcp port 143 but the IMAP dialog is not the same as the 
       POP3 dialog. They are defined in RFCs.

POP3s and IMAP4s: They are the "Secured" version of POP3 and IMAP4 (so most
probably what Claws is using on your machine). It starts with a TCP
connection (as above) but then a secure layer (SSL/TLS) is established to
encapsulate and protect all the dialog between the "applications" - hence
avoiding passwords transmitted in clear text).
You can use openssl to test (exemple with POP3):

187 [15:44] rol at riri:~> openssl s_client -host riri.xxx.xxx -port 995
......
+OK ready  

(I've hidden all the "s" dialog).

Paul

-- 
Paul Rolland                                E-Mail : rol(at)witbe.net
CTO - Witbe.net SA                          Tel. +33 (0)1 47 67 77 77
18 Rue d'Arras, Bat. A11                    Fax. +33 (0)1 47 67 77 99
F-92000 Nanterre                            RIPE : PR12-RIPE

Please no HTML, I'm not a browser - Pas d'HTML, je ne suis pas un
navigateur "Some people dream of success... while others wake up and work
hard at it" 

"I worry about my child and the Internet all the time, even though she's
too young to have logged on yet. Here's what I worry about. I worry that 10
or 15 years from now, she will come to me and say 'Daddy, where were you
when they took freedom of the press away from the Internet?'"
--Mike Godwin, Electronic Frontier Foundation 
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