'Letter' in the Bible

not to be so quickly upset or alarmed when someone claims that we said, either by some spirit, conversation, or letter that the Day of the Lord has already come.

So then, brothers, stand firm, and cling to the traditions that you were taught by us, either by word of mouth or by our letter.

If anyone does not obey what we say in this letter, take note of him. Have nothing to do with him so that he will feel ashamed.

I, Paul, am writing this greeting with my own hand. This is the mark in every letter of mine. It is the way I write.