epistolographic

from The Century Dictionary.

• Pertaining to the writing of letters.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Pertaining to the writing of letters; used in writing letters; epistolary.
• adjective the same as Demotic character. See under Demotic.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Relating to the writing of letters
• adjective Characteristic of a letter