Can any other birds besides the carrier pigeon be trained en mass to carry letters?

What was so special about carrier pigeons, and why haven't we trained any more? Could other birds do that job, like crows? Thanks for your feedback.|||in the arabic coulture it has been know to use falcons to send letters to distant people. and back in the dark ages it was a common occurance too.|||Crows are intellegent enough but owls were widely used by the English.|||yes falcons can be trained to carry and send letters, it has been used by the arabs for many years