It's about one-nine-hundred-thousandth the number of Chickens in the World.
In other words, 21,000 is 0.00000110 times the count of Chickens in the World, and the count of Chickens in the World is 910,000 times that amount.(a.k.a. fowl) (Gallus gallus domesticus) (2011 figures) (average population)
The most numerous domesticated animals in the world, the estimated average population of chickens worldwide is 19 billion animals. Of these, about 6.4 billion birds produce the world's supply of chicken eggs.
It's about 0.00000007 times the number of Emails Sent per Day.
In other words, 21,000 is 0.00000007140 times the count of Emails Sent per Day, and the count of Emails Sent per Day is 14,000,000 times that amount.(2010 figures) (estimated averages)