Here is a model letter from Libanius (1 in the Loeb; 15 in the Foerster Teubner). Yes, Libanius is (allegedly) writing a letter about how he is no longer going to write letters.
1 To Zenobius
“I have decided to fight silence with silence. Indeed, I do still understand that this penalty falls short of the wrongs done to me: It is not the same for me to be bereft of your letters and my letters to fail to go to you. The harm I suffer is as much greater than my vengeance as your letters are better than mine.”
Σιγῇ τὴν σιγὴν ἔγνωμεν ἀμύνασθαι. καίτοι γε ἠπιστάμην λειπομένην τῶν ἀδικημάτων τὴν δίκην. οὐ γὰρ ἴσον ἦν ἐμὲ σῶν ἀποστερεῖσθαι γραμμάτων καὶ σοὶ <τὰ>1 παρ᾿ ἡμῶν μὴ φοιτᾶν. ἀλλ᾿ ὅσῳ καλλίω τὰ σά, τοσούτῳ μείζων ἡ βλάβη τῆς τιμωρίας.