This article in the Jewish Encyclopedia indicates that the rulers of Jerusalem in the first and second centuries had delegates called "Apostoloi" that would be charged with carrying about circular letters:
...Apostle (Greek ἀπόστολοσ, from ἀποστήλλειν, "to send"), a person delegated for a certain purpose; the same as sheliaḦ or sheluaḦ in Hebrew, one invested with representative power. "Apostoloi" was the official name given to the men sent by the rulers of Jerusalem to collect the half-shekel tax for the Temple, the tax itself being called "apostolé." See Theod. Reinach, "Textes Grecs et Romains, etc.," 1895, p. 208, and also Grätz, "Gesch. der Juden," iv. 476, note 21, where Eusebius is quoted as saying: "It is even yet a custom among the Jews to call those who carry about circular letters from their rulers by the name of apostles"; Epiphanius, "Hæreses," i. 128: "The so-called apostoloi are next in rank to the patriarchs, with whom they sit in the Sanhedrin, deciding questions of the Law with them." The emperor Honorius, in his edict of 399, mentions "the archisynagogues, the elders and those whom the Jews call apostoloi, who are sent forth by the patriarch at a certain season of the year to collect silver and gold from the various synagogues" ("Cod. Theodos." xvi. 8, 14, 29. Compare Mommsen, "Corpus Inscr. Lat." ix. 648. See Apostolé).
Might there be any examples extant of such circular letters?