Etymology From Middle English letterly, equivalent to letter + -ly.
1
Befitting or characterised by letters (posted messages).
The context, it is worth noting, is a letterly one of postoffices, envelopes, and mailings.2002, James G. Watson, William Faulkner: Self-Presentation and Performance, page 65:
At times Faulkner wrote himself into his fiction by the letter writers he created; and often enough he wrote himself out of it by the content and style of their miswritten letters. The juxtaposition of his literary and letterly writing is revealing of both canons.2014, James G. Watson, William Faulkner, Letters & Fictions:
letterly
adv
Etymology From Middle English letterly, equivalent to letter + -ly.
1
In a manner befitting or denoting letters; to the letter; precisely.
Christian Scientists, all over the world, who are letterly fit and specially spiritually fitted for teachers, can teach annually three classes only. They shall teach from the Christian Science textbook.1924, Mary Baker Eddy, Miscellaneous Writings 1883-1896 (Authorized Edition): - Page 316: