How to Understand Date and Time in Email Headers

Businessman checking the time on his watch
This is one time; In emails, time and date might look different. StockUnlimited

When an email is sent, it passes through mail servers, a handful perhaps. Time and again, each of these servers finds the time to record the current time—and the date, too—in the email's paper trail: its header area.

Looking at these header lines, you can find out when an email was sent, where it was delayed and maybe how long it was held up. To understand the dates and times in email headers, you may have to compute a bit, though, using easy math.

How to Understand Date and Time in Email Header Lines

To read and interpret the date and time found in email header lines:

  • Look for date and time in lines beginning with Date: and Received:.

    Note: The "lines" in the email header area can continue on the next line on the screen with indentation.
  • The format for date and time is Day of the week, Day Month Year Hour:Minute:Second +/-Time zone offset.

    The individual parts use the following format:
    Day of the week — the weekday's name in 3 letters: Mon, Tue, Wed, Thu, Fri, Sat, Sun
    Day — the day of the month in numbers: 1-31
    Month — the month's name in 3 letters: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec
    Year — the year after 1900 in 4 digits: 1900
    Hour — the hour of the day in 2 digits: 00-23
    Minute — the minute of the hour in 2 digits: 00-59
    Second — the second of the minute in 2 digits: 00-59
    Time zone offset — the difference of the time given to UTC/GMT in HourMinute, preceded by + if the time is ahead (east) of UTC and preceded by - if the time is behind (west) of UTC: −2359 to +2359
    UTC itself appears as +0000; −0000 means the time zone essentially unknown.
    Sometimes, the time zone's name will appear as part of the time zone offset (like +0000 (UTC)); you can ignore that.

    How Can I Convert the Date and Time to My Time Zone?

    To convert the date and time to your time zone, do the following:

    1. Subtract any + time zone offset from the time or add any - time zone offset to the time
    2. Do pay attention to the date: if your result is greater than 23:59, add a day and subtract 24 hours from the result; if the result is less than 0, subtract a day and add 24 hours to the resulting time.
    1. Add or subtract your current time zone offset from UTC.
    2. Repeat the data calculation from step 2.

    You can also use a time zone calculator to easily compute the date and time for any place on earth, of course.

    Email Header Date and Time Example

    Sat, 24 Nov 2035 11:45:15 −0500

    1. Adding 5 hours makes this Saturday, November 24, 2035, 16:45:15 UTC — 4:45 pm in London, for example.
    2. Adding 9 hours to that UTC time and date for JST (Japan Standard Time) gets us 01:45:15 in the morning of Sunday, November 25, 2035 in Tokyo, for instance.
    3. Subtracting 8 hours from UTC for PST (Pacific Standard Time) makes 08:45:15 back in the morning of Saturday, November 24, say in San Francisco.

    That date and time could appear in an email's headers as:

    • Date: Sat, 24 Nov 2035 11:45:15 −0500
    • Received: from mailer01.example.net (mailer01.example.net [192.168.01])
          by ixde-df8.example.com (Internet Inbound) with ESMTP id 44524380000AA
          for ; Sat, 24 Nov 2035 11:45:15 −0500 (EST)
    • Resent-Date: Sat, 24 Nov 2035 11:45:15 −0500
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