How to prove that email sent on certain date of outlook

Recently I asked my colleague to send an email on Friday(4th October 2013). He failed to send me a mail on that day.

He simply changed the system date and time to Friday and sent me a mail on Monday yet it appears in my email client that it was sent on Friday. Is there any way to prove that he sent the mail on Monday?

I looked at his sent items but it shows Friday's date. I need to prove that he made the system date time to send me a mail on Monday. Both of us were using Windows 7 32 bit operating systems.

How to prove when the email was sent?

The email headers will show the timestamp of the message when it was handled by each mail server, very likely this will include your correspondent's SMTP server (his ISP's server) and your server (one or more of your ISP's servers).

To access the email headers in your copy of Outlook read this guide.

The header of the email could give you that information, as each mail server the message passes through adds the time (based on the server's clock) that the message was received on that leg of the journey to your machine.

If you can't see the full header of the email, here are directions for finding this setting in all versions of Outlook.

Microsoft has a breakdown of how to read their Outlook headers here.

From that Microsoft page, the field you'll want to look at is X-OriginalArrivalTime, as:

This is a time stamp placed on the message when it first passes through a server running Microsoft Exchange.