Re: How to use port 465 ?

Sam Varshavchik <[email protected]> Thu, 29 May 2025 22:32:25 -0400
Newsgroups	gmane.mail.imap.courier.general
Message-ID	<[email protected]>
Mike Wright writes:

> Greetings,
>
> My new ISP blocks port 25 (hard block at network level; no overrides)
> so I have to use 465 instead.  (I've never used port 465 before and
> don't know anything about using it.)  Port 465 in the firewall has
> been opened.  Mail client is Thunderbird.  SMTP settings are  465,
> STARTTLS, no authentication.  Attempt to send mail eventually times
> out with error :
>
> (server nicname is OLI)  ...connection to Outgoing server (SMTP) OLI timed  
> out
>
> Two terminals opened 1) is running tcpdump -i eth0 port 465 ; 2) has
> executed this script :
> addcr | TLS_VERIFYPEER=NONE couriertls -host=<OLI> -port=465
> -protocol=smtp -printx509=2  (found in email from Krystal back in Sep
> 2023).  /etc/courier/smtp/esmtpd-ssl has line #79 ESMTPD_LOG_DIALOG=1
> but there is nothing showing in the journal or syslog.
>
> 1) shows connection established with SYN,SYN-ACK,ACK then nothing
> until client gives up and server sends an F-ACK, P-ACK, F-ACK and
> client responds with R, R.
>
> 2) produces no output for minutes then produces this cryptic output :
> "select: No such file or directory"
>
> But the server does respond ; telnet OLI 465 produces :
> Connected to oli.
> Escape character is '^]'.
>
> No idea where to go from here.

Find the process that's listening on port 465:

fuser -n tcp 465

Now, attach strace to this process

strace -s 256 -p <pid>

Now, make a connection attempt to port 465. The strace command should  
produce some output, in response to that.

This will determine whether the server is receiving a connection, or not.  
That would be the first step. An extra bonus is would be

ls -l /proc/<pid>/exe

and verifying that this is a symlink to couriertcpd.

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