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Re: [ietf-smtp] [dispatch] Forced SMTP redirects

2021-03-16 20:05:09
I have some dim recollection of very, very few instances, over the last 
several decades, of parties who were (apparently) very much invested into 
having their mail delivered, trying to convince me that someone telling them 
5xx didn't really mean that, because of the specific error message that was 
assigned to the specific numeric code. I never found those arguments very 

The most innovating argument revolved around the interpretation of "in the 
same sequence". The argument was that it only means "hey, you just can't 
resend it immediately, but if your RSET, or maybe disconnect or reconnect, 
its okay-dokay".

Postfix does give the MTA administrator some rope to hang himself with via
SMTP "reply filters" that allow transformations between arbitrary [45]xy
codes to other code (typically 5xx -> 4xx) allowing them opportunities
to retry some hard error with a problem peer, or perhaps fall back to
an backup relay.  That leaves any matching of codes and reply text to
the user...

... What dogs hear ... 


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