'Letter' in the Bible

that you not be easily shaken from your composure, nor be troubled either by a spirit or by a message or by a letter {alleged to be from us}, to the effect that the day of the Lord has arrived.

So then, brothers, stand firm and hold fast to the traditions which you were taught, whether by [spoken] word or by letter from us.

But if anyone does not obey our message through this letter, take note not to associate with him, in order that he may be put to shame.

The greeting [is] by my hand, Paul's, which is {a sign of genuineness} in every letter: {this is how I write}.