epistolical

from The Collaborative International Dictionary of English v.0.48

Epistolic \Ep`is*tol"ic\, Epistolical \Ep`is*tol"ic*al\, a. [L.
   epistolicus, Gr. ?.]
   Pertaining to letters or epistles; in the form or style of
   letters; epistolary.
   [1913 Webster]