To change the sender address on an event custom suggested message do the following: 
  1. Choose Edit Under "Actions" in the TeamRaiser list for the appropriate event
  2. Click Select Event Options. 
  3. Click Edit Advanced Options, under Related Actions in the left column.
  4. Click Define Event Options. 
  5. You can change that address on that page, by changing what is in the Sender Email Address option.