Epistolary

[Grogie]

Relating to letters or missives. ''They had a long-distance, epistolary friendship.''

[Slava]

An excellent suggestion from the world of Grogie, and not one of the more arcane to come from there. It's actually a common form of novel writing, and turns up rather often in biographies and the like.

The sending of Christmas cards, at least here in the States, is often the only physical form of epistolary communication we practice with any regularity.