[WWI] Not complaining....but

Shane Weier bristolf2b at hotmail.com
Wed Aug 18 16:39:37 EDT 2004

Neil says

>Don is correct, even for us who are in mail mode (not digest),
>mails often arrive in the wrong order. It's pixie magic.

Back when I had a day job, I was responsible for email performance for my 
global employers, so I have a reasonable understanding of what's happening. 
Simplified slightly because I don't want to be more than usually boring this 
is what happens...

When you send an email, it goes from your PC to a mail server at your 
service provider (ISP). To get to the destination it has to be passed 
through a chain of mailservers, some (maybe) belonging to the same ISP, 
mostly not. It's designed to be pretty bombproof, so if the data 
communications between any of the servers is down for some reason the email 
will be held and the server keeps trying until it gets through.

But...if the line is down for a while one of several mechanisms can cause 
your email to arrive out of order.

If it's stored as it arrives (like stacking plates) and then sent by taking 
the last arrived email and sending it on, then the next to last (like 
unstacking plates) all the emails that were held will be sent in reverse 

Or, the delayed mail can be reroutedby a slower path. If the original fast 
link comes back up again the next (later) emails will go the fast route and 
get to you first.

or, even when things are working properly, where there are multiple paths, 
some emails will go the fast way, others will go the slow way and arrive out 
of order.

But the should all arrive, and usually do, to an order of reliability which 
in the context of the billions of emails flowing around is amazing even to 
someone who spent his life working on data comms


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