Re: How to use port 465 ?

On 30/05/2025 05:21, Lindsay Haisley wrote:
> On Thu, 2025-05-29 at 15:37 -0700, Mike Wright wrote:
>> 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 :+
> 
> Port 25 is considered a "server to server" SMTP port, and frequently
> blocked for MUA use, especially on public access points, and
> increasingly by ISPs.


That's historical.  465 was the URL Rendezvous Directory (URD) for 
Source Specific Multicast (SSM)


> The appropriate port for MUA (mail user agent) connection these days is
> port 587, considered the "mail submission port", as per RFC-4409.
> 
> See <https://www.rfc-editor.org/rfc/rfc4409https://www.rfc-editor.org/rfc/rfc4409>


RFC 4409 is obsoleted by RFC 6409.  RFC 6409 is modified by RFC 8314:
https://datatracker.ietf.org/doc/html/rfc8314


> Unlike Port 25, use of port 587 requires authentication from the client
> end. Port 587 supports TLS natively and STARTTLS as well.


Ditto for 465.  The point was that a man in the middle can somehow hide 
the STARTTLS keyword from the SMTP greeting, thereby forcing the user to 
a cleartext session.  Port 465 starts encrypted, like 443 for the web, 
so you need no STARTTLS,


Best
Ale
-- 







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