Besides the To, Subject, Cc, and Bcc fields in the Format menu of a Compose window, you may want to add your own fields, such as Reply-To, Return-Receipt-To, and so on.
Choose Compose Window from the Options menu.
The Compose Window Options dialog box is displayed.
Type a name in the Header Name field as it will appear in the Compose window header (for example, Return-Receipt-To).
(Optional) Type a default entry for the defined header field in the Default Value field (for example, your email address).
Click Add to add the values to the scrolling list.
To change a custom field, select it and edit the Header Name or Default Value field, as appropriate, then click Change.
To remove a custom field, select it and click Delete.
Click OK or Apply to make your changes take effect.