In PoliteMail version 4.951+ you are now able to edit your preheader text.
Outlook Message Preview
Preheader text is the text that appears under the Subject line in the Outlook Preview pane. It's the first few lines of the body of your email, but it can also be security notifications such as External Sender alerts.
Outlook allows you to display up to 3 lines of preheader text. To change this setting, go to Outlook > View > Message Preview.
How to Edit Preheader Text
It's important to keep in mind that your custom preheader text will only be displayed based on the recipient's Outlook Message preview settings. PoliteMail tracking must be turned on in order to display custom preheader text.
Open a new message in PoliteMail and turn tracking on. Click the PoliteMail tab and you will see Edit Preheader text under the HTML options.
Now you may enter up to three lines of Preheader text which will be displayed in the recipient's reading pane once they receive the message.
If you uncheck the "Custom Preheader Enabled" box, your message will be received with no preheader text. However, viewers will still be able to see the first line of the email.