Outbound Order and Priority [was Re: Recipient is offline]

Tony Finch wrote:

> Exim has a database of which messages are waiting for which hosts, so 
> when a host comes back to life it can flush the messages down the 
> same connection without having to wait for the next queue run.
This brings up a side point when host collection, sorting and queuing 
is done.
I only suggest this as reasonable explanation for this example 
observation.
In this list and others, like IETF, I noticed the my subscription 
address with a host to santronics.com, takes am extremely long time 
for one of my messages to get posted. Sometime its pretty quick like 
within the hour for IETF-SMTP, IETF-DKIM but it could be many hours to 
half a day to even the next day.  For the IETF list, it is perpetually 
worst and I have seen my santronics.com take 2-3 days before it is 
posted.  When I saw that, I asked the list operator and he indicated 
appeared to be a problem somewhere he could not explain and could not 
address yet until he return from a business trip.
I asked about queuing and he wasn't sure what the special magic was. 
So I subscribed with my junk alias gmail.com alias and now all my post 
come in pretty fast in both IETF-SMTP and IETF list within the hour or 
so.  That is why I have been posting with my gmail account.
So I suggest that the software is collecting, sorting and probably 
maybe related to total counts, like gmail.com addresses and others 
common subscription addresses, that it spawn delivery job based on the 
highest count first and the single host mail as done last and maybe 
alphabetically.  I suppose total failure history to connect is a 
factor, but our MX servers are rarely ever down.
The only point here is to express another reason why we choose to send 
mail out autonomously, equally as they come for the highest efficient 
and throughput. When you  priority based on counts, etc, the majority 
which are count=1 host mail will be delayed far longer than it has to 
been.
The only time wcSMTP stops and blocks a host domain is with NXDOMAIN 
or connect failures attempts is exhausted.   We provide operators a 
URL link to removed them off the block list.  This only happens with 
non-full time low end operators and sites.  ETRN will not work at this 
point for any old mail that was already bounced.
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