Email timestamps: is this how they work?

Factual Questions
1

I’m trying to learn how the time & dates get attached to email messages. From what I can tell, when a user sends an email, the timestamp is picked up from his computer, so the accuracy is dependent upon his PC’s clock. This is the “sent” time as displayed in Outlook.

When the message arrives at the final destination server (not user), it is timestamped according to the server’s internal time. This is the “received” time as displayed in Outlook.

These times don’t get changed thereafter, but are imbedded in the header info.

If the recipient views a message using a web-based email viewer or a download-style program like Outlook, he will see the timestamps as above no matter when he actually views or downloads them.

Is this the way things work?

The reason why this is important is I think some of my incoming mail is being delayed by one or more forwarding services, sometimes for hours or even days if I interpret the timestamps right.

2

Almost forgot. I assume all timestamps use local time, including Daylight Saving Time if appropriate. So if I were to calculate the time differences between sent and received times, I would have to know what zones each one came from, right? That could be tough if I don’t know where an email server is physically located.

3

This is broadly correct.

4

Two things that might be worth noting, given your stated purpose: Under normal circumstances, each mail transport agent, which broadly means “server”, will place a timestamp in the message headers indicating the time of receipt. It’s not just the first and last one, but each one in between as well. Pretty good example here. If something is delaying your e-mail, these header lines are the place to look first.

Also, each timestamp contains information identifying the time zone; while they may be wrong, they’re not ambiguous. In the example cited, the last field of the timestamp, the ones that look like “-0400” represent the timezone, or more specifically, the offset from UTC.

5

Thanks, I’ve been wanting more info on this for a long time. Let’s take, for example, the first one in your cite, which is


Sat, 24 Sep 2005 15:26:43 -0400

I suspect that this could be translated as “the moment which was called 3:26:43 PM Standard Time in the time zone of Halifax NS Canada, but they were on summer time in September, and it is also the same moment as what they called 3:26:43 PM Daylight Time in New York City USA.”

Am I close? Or does the “-400” refer to the east side of Greenwich?

6

You’re right. Right now in NYC it is 4 hours behind GMT (-4). In Abu Dhabi it’s +4.