Email headers are very useful in troubleshooting any issue related to email, from tracking spam to correcting catchalls and bounced messages.

To view email headers in webmail, there is a "Full Header" link located on the top right corner.

Different email clients also allow you to view headers:

Outlook -- Right click on the message, select "Options," header information is located in "Internet Headers" text field.

Outlook Express -- Double-click on the message, select the "File" menu, click "Properties" and "Details."

Apple Mail -- Double-click on the message, choose "View," select "Customize Headers" and drag the "Show Headers" icon into your toolbar.

Entourage -- Double-click on the message, select the "View" menu, click "Internet Headers" and use your mouse to pull down on the line below the header so that the entire header is visible.

Eudora -- Double-click on the message, click the button on the upper left-hand corner of the message.