I have more than 1 delivery server set up in my system. When I log into my customer account to send a campaign to my lists, how do I choose the delivery server I want to use to send the email to that list?
First, you need to allow this from Backend > Settings > Customers > Servers > "Can select delivery servers for campaigns". (if customers are part of a group, do it from group settings, same path).
Once you do this, the servers will appear in the setup step of the campaign for you to choose from.