I think I’ve figured out a way to control what your pre header text says in your email, even when using Convio, a popular email software for non profits.
Preheader is short summary text that follows the subject line. Many mobile, desktop and web email clients show pre headers to tip readers off on what the email contains before they open it. In the attached image “This Saturday: Auto Auction” is the pre text in Outlook. 
1. Login to Convio and go to Email> Stationery. Find the Stationary of the email you want to add Pre Header text to.
2. Click Edit
3. Click 3. HTML
4. Switch to HTML view (Edit HTML Source)
5. At the top, add this code
7. Test it out by sending yourself a test email.
This allows you to have Pre Header text that won’t affect your design because the text will be white.
If you have questions, email me at debbie.gillum@voago.org
Debbie Gillum Wakefield 