Sometimes our support team will ask you to send over your email headers. This helps us troubleshoot issues with delivery. The following links will help you find your header information in various email programs.
Finding your headers in Outlook 2007:
http://office.microsoft.com/en-us/outlook-help/view-e-mail-message-headers-HA001230300.aspx
Finding your headers in Outlook 2002 & 2003:
http://office.microsoft.com/en-us/outlook-help/view-e-mail-headers-HA001093707.aspx
You can find Gmail, AOL, Windows Live (desktop and hotmail) and Yahoo! here:
http://blog.deliverability.com/2010/03/where-the-are-the-headers.html
Spamcop has additional resources on header information here:
http://www.spamcop.net/fom-serve/cache/19.html