A Thankster drip campaign is a series of mailings that you set up ahead of time by creating a series of templates for cards, letters, or notes, and specifying when they will go out. These will be mailed to the recipients on a Thankster list that you specify.
For example, you might set up a welcome campaign, consisting of a sequence of informational and promotional mailers you want new customers to receive. It would kick off after a user signs up for your product, or places their first order. The first one might be a folder thank you card, standard size, welcoming them and thanking them for signing up. This could be followed two weeks later by a flat card or postcard that has a promotional offer, and then perhaps three weeks later a letter with a photo of a product you would like to upsell.
Other drip campaign ideas would be to start a sequence on a birthday, or home purchase anniversary. There are limitless possibilities.