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Glenn,

HELO groupmanagersforum.groups.io

LOL!

The typical way of scaling such things is to use horizontal scaling
with a load balancer front end that has session traffic marking.

This sounds like a description of inbound load balancing, but I imagine that outbound sort-of mirrors it.

I know that Yahoo Groups' outbound system sorted the traffic by destination domain and generally sent batches of messages to each domain in order to reduce transaction overhead. They also used a fleet of outbound servers (physical, in the day, possibly virtual later) covering a large number of IP addresses - something Lena has tracked over the years, and which at one time was listed here to help mail services with whitelisting them:


But Groups.io is built out of much more modern stuff (hardware and software), and as yet anyway likely carries much less traffic, so its structure is likely much different.

All of a transaction usually takes only seconds,

Back in March Mark commented that outbound traffic was peaking near 5M messages per day, which is something like 60 per second. So clearly a fair amount of parallelism is required in the transaction handling. And would be anyway, just to avoid stalling on a particularly slow destination server.

Whether that load can be handled in a single modern-day server, or requires multiples, and in the latter case whether the multiples can hide behind some form of edge concentrator to appear as a single outbound IP address is where my curiosity lead.

Where it has an impact on we users is when destination services use IP-based filtering, and need to maintain a whitelist or reputation database. As apparently is the case with Outlook/HotMail. In the extreme case you end up with something like Yahoo Group's server list that must be published. Though from what Mark (and the posting cited below) said it seems there are now more official "back channel" ways to communicate server addresses between senders and receivers.

Before Lena's answer I thought perhaps the cited IP address might have been a new one, causing the disruption because it was unknown to Outlook/HotMail. That is, I thought this might have been an instance similar to this (though years old):


But if there's only been one Groups.io outbound IP then that's not Outlook/HotMail's excuse.

Shal


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