'Service' in the Bible

And he wrote the name of king Ahasuerus, and sealed it with the king's ring, and sent letters by post on horseback, riding on swift steeds that were used in the king's service, bred of the stud:

So the posts that rode upon swift steeds that were used in the king's service went out, being hastened and pressed on by the king's commandment; and the decree was given out in Shushan the palace.