This is a copy of the letter which they sent to Onias: This verse is properly indented in Good News Bible, since it is part of the letter that began in verse 6, but it is a paragraph of its own, since it introduces the letter referred to in verse 7. The translation of this verse should make it clear that what follows is the old communication, and not something new. Revised Standard Version can leave readers quite confused, since they would naturally assume the pronoun they refers to Numenius and Antipater, which it does not. A helpful model for this verse is

• “The following [or, Here] is a copy of the letter your people sent to Onias [long ago].

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on 1-2 Maccabees. (UBS Helps for Translators). New York: UBS, 2011. For this and other handbooks for translators see here.