'Letters' in the Bible

I said to the king, "If the king is so inclined, let him give me letters for the governors of Trans-Euphrates that will enable me to travel safely until I reach Judah,

Then I went to the governors of Trans-Euphrates, and I presented to them the letters from the king. The king had sent with me officers of the army and horsemen.

In those days the aristocrats of Judah repeatedly sent letters to Tobiah, and responses from Tobiah were repeatedly coming to them.

They were telling me about his good deeds and then taking back to him the things I said. Tobiah, on the other hand, sent letters in order to scare me.