He wrote letters in the name of King Ahasuerus, sealed them with the king's ring, and sent them by mounted couriers riding on fast steeds bred from the royal herd.
References for Esther 8:10
By these letters the king allowed the Jews who were in every city to assemble and defend their lives, to destroy, to kill, and to annihilate any armed force of any people or province that might attack them, with their children and women, and to plunder their goods
on a single day throughout all the provinces of King Ahasuerus, on the thirteenth day of the twelfth month, which is the month of Adar.
A copy of the writ was to be issued as a decree in every province and published to all peoples, and the Jews were to be ready on that day to take revenge on their enemies.
So the couriers, mounted on their swift royal steeds, hurried out, urged by the king's command. The decree was issued in the citadel of Susa.
Then Mordecai went out from the presence of the king, wearing royal robes of blue and white, with a great golden crown and a mantle of fine linen and purple, while the city of Susa shouted and rejoiced.
For the Jews there was light and gladness, joy and honor.
In every province and in every city, wherever the king's command and his edict came, there was gladness and joy among the Jews, a festival and a holiday. Furthermore, many of the peoples of the country professed to be Jews, because the fear of the Jews had fallen upon them.