On 2020-12-17 18:17, L. Mark Stone via mailop wrote:
Hi John,
Unfortunately, many sending clients (newsletters, announcements, etc.) do not
retry if the initial delivery fails. So if your primary MX has network issues,
doesn't comprise a load balancer in front of multiple MTAs and you are doing
system maintenance, you can lose emails in the absence of a secondary MX. Like
if your corporate domain was on Gmail earlier this week, for example.
I think the "many" is now very few. Back in the day, everybody had to
write their own client, or think something like Perl's Net::SMTP was the
bee's knees all by itself.
Not only do they not queue/retry, in many cases their RFC compliance
sucks, and they get dinged by blacklists like the CBL/XBL. (Net::SMTP,
without careful use, WILL get you listed. As will several other similar
libraries).
In my circles, we refer to these as "idiots with keyboards". They know
enough to be dangerous.
What has happened since this time is that with default/mandatory port 25
blocks in so many places (including web hosting), and those that don't,
usually get blacklisted (by bad clients, or more likely infected
malware), that they quickly turn out to be not worth using. They
certainly won't work thru grey-listing either.
Instead, web hosters are offering outbound queuing thru supported
servers, managed email environments (thru gmail, or more traditional
ESPs) make things so much easier, and don't need any idiots with
keyboards. The idiots with keyboards mess something else up.
[This is not to say that Net::SMTP and the like have no place. I still
use it, but only in very specific circumstances where fail to queue is
not an issue as long as I get an error.]
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