The gist is: For flexible funding campaigns the amount given via PayPal are transferred directly to the campaigns PP account (minus the fees obviously). For fixed funding campaigns the given amount is transferred after the campaign meets the funding goal. Money given via direct Credit Card payment will be cashed out after the campaign reaches its deadline and should arrive within 15 business days.

Mailpile is a flexible funding campaign, so the first rule applies and funds are directly placed in their PP account.