All pages of a mail form are customizable.
Like post forms, mail forms have separate Compose and Read pages. When a user opens a new mail message, the form is displayed in Compose mode and pages are displayed so that the user can fill out the form to be sent. When the recipient opens the item, the form is displayed in Read mode, and a different set of pages and controls can be used to display the data in the fields. When designing a mail message form, you can choose to disable the separate Read and Compose pages so that the form is identical at all times. If you use separate pages, you can often copy and paste the controls from the one set of pages to the other.
Learn about making separate Compose and Read pages
If you are customizing a mail form for use in an organization that is using Microsoft Exchange Server, the form should be published in the Organizational Forms Library. If you do this, then you can clear the Send form definition with item check box on the form's Properties page so that only the field data is transmitted when the item is sent. This will greatly reduce network traffic and also make updating the form much easier in the future because each client will be using the shared form that is published on the server.
When designing a mail form, itÆs important to consider which type of message format the form should be in. Choices include Microsoft Rich Text, HTML, or plain text. Careful consideration should be given to what versions of Microsoft Outlook or Word potential recipients will be using. To programmatically set HTML in a mail form, see HTMLBody Property. To programmatically access the Word object model to manipulate a Word mail message, see WordEditor Property.
Note Some of the properties and objects related to mail formats may behave differently depending on the server you're using.