[SWLUG] Is this working?

[Dave Cridland]

On Wed May 27 18:58:35 2009, Neil Jones wrote:
> The time of sending is encoded into the headers and email reading
> programs use it.

Since this comes up from time to time, I'll stick my "email expert"  
hat on, and explain things, since this is slightly incorrect, and  
we're a technical group, right?

A typical email has three sources of "the date".

There's the "Received date", which isn't in the message itself - it's  
metadata controlled by the store, like IMAP's INTERNALDATE, or the  
"From" line on a Berkeley mbox file. It's stamped on by the store on  
delivery.

There's the "Date" header field - I'll be fussy and point out each  
message has but one header, which has multiple fields - which is  
created (hopefully) by the Sending MUA (Mail User Agent, or email  
client). This is quite often a fairly creative interpretation of the  
time, but usually represents when the email was completed - but not  
sent. Thunderbird, for instance, applies the Date header prior to  
sending, which you'll see most obviously in offline usage.

Then there's the "trace header fields", which for our purposes really  
means the Received header fields. One gets added by each MTA (Mail  
Transfer Agent - email server) the message passes through.

The very first one on Neil's message, for instance, gives 18:58:40  
+0100. This is fairly reliable, since most servers have synchronized  
clocks, using NTP or similar. (Most Linux workstations do, too,  
mind). This is when Neil actually sent the mail - some 5 seconds  
after he wrote it - and it's this timestamp you need to check delay  
on.

Neil's message was delayed by 39 seconds before swlug.org got it, but  
stayed there for around 47 minutes, probably passing in and out of  
mailman, and then a futher 5 minutes before Google accepted it for  
me. (My email routing being hideously complex). It then rattled  
through the next *cough* 10 servers without incident, finally  
arriving at my IMAP server a couple of seconds after that.

Hope this vaguely explains things. :-)

Dave.
-- 
Dave Cridland - mailto:dave at cridland.net - xmpp:dwd at dave.cridland.net
  - acap://acap.dave.cridland.net/byowner/user/dwd/bookmarks/
  - http://dave.cridland.net/
Infotrope Polymer - ACAP, IMAP, ESMTP, and Lemonade