Re: [Mailsec] CLIENTID with PIPELINING

Michael Peddemors <michael@linuxmagic.com> Thu, 16 March 2023 15:42 UTC

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Subject: Re: [Mailsec] CLIENTID with PIPELINING
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On 2023-03-15 15:37, Andrew C Aitchison wrote:
> 
> [ Apologies if this doesn't thread properly.
>    My MUA doesn't have access to the message to which I am replying. ]
> 
> Michael Peddemors:
>>  in my humble opinion, when advertising CLIENTID support, it
>> should NOT advertise PIPELINE support
> 
> I have options for each of PIPELINE, PIPECONNECT* and CLIENTID
> just to advertise to selected hosts (default *)
> but how else could I determine which to use ?
> Two options I can see:
> 1 prefer PIPELINE in plain and CLIENTID when encrypted, or
> 2 CLIENTID in SUBMISSIONS (port 465) but PIPELINE on port 25 ?
> Any other thoughts ?
> 

Of course, CLIENTID MUST be only over encrypted channels.
And while some operators may still allow authentication over port 25, as 
an industry we treat that as historical, and only allow authentication 
over port 465 (SSL) or 587 (TLS)

Suggest that you ONLY support CLIENTID on the submission ports.

Recommend that you only advertise PIPELINE on port 25, if you choose to 
do so. While MTA's might have a reason NOT to advertise PIPELINE any 
more, there are still use cases (eg internal relays etc) that are not 
affected by PIPELINE.  IMHO, PIPELINE advertisement should not be on by 
default, but that is another topic.

More feedback by the Exim community might be in order, but as to 
CLIENTID, suggest you ONLY advertise CLIENTID on 465/587 by default, and 
ONLY if the connection is encrypted.  (Some MTA's out there still allow 
submission over port 587, with STARTTLS optional)



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