@ClosetCleanoutCrew asks
my packed card is a little stiff and thick. Can I still mail it like an ordinary letter?
Jeff answers
I'd measure the completed package and check the carrier's current requirements for the exact service. Don't choose postage solely because the contents are a card. The holder and padding affect how the package is handled. Getting the mailing category right is part of protecting the item.
— Jeff, infinitepulls.com