To isolate and resolve problems with emails or to block a phishing attempt, it is often necessary to view the technical information that is contained in the email's letterhead, also known as header information. In most cases, it may be necessary to forward this information. In the following, instructions for how to display this information in the various email programs can be found.

Outlook 2010 (Windows 7)
Double-click the email in the inbox to open it in a new window. Go to the File tab in the new window and click on the Properties button. The extended headers can be found in the field Internet headers.

Outlook 2011 (Mac)
Right-click the mail in the inbox, and then select View Source.

Mail OSX in Lion
Select the email in the inbox. Now select View in the toolbar, and then Message and Long Headers. Alternatively you can use the shortcut ⇧⌘H.

Webmail (Outlook Web App)
Double-click the message in the inbox to open it. Then click the Message Details icon (an envelope with a small document over it).

Hotmail
Click on Options on the navigation bar on the left-hand side. From the page Options, click on Preferences, scroll down to Message headers and select Full.

Gmail
Open the email. Then click on the arrow (More) next to the reply icon and select Show Original.