It's almost instant no matter where you're from.. Sometimes when its slow it could take up to five minutes depending on how busy the servers are. But its definitely very fast within the hour at the most.
Email delivery takes less than a second to reach from one place to any place in the world. In reality, you don't know what is the physical place of the email server. For example, yahoo server is in America. When you send an email from Russsia or India then it goes to America within no time. The person who open his/her email in Russia, India or Africa etc is actually fetching the data from America.
It will arrive immediately. But there are times where the mail takes a
few hours or even days to arrive. Sometimes you just need to refresh
your browser...
for email related queries and questions, you can contact webmailhelps.
It all depends on how fast your FBI agent reads (just kidding). As already mentioned, distance has no effect on this. Your message can be read in many hours later only because when it is day in the USA, in Russia it is already the night of the next day. It can really slow down communication, especially when it comes to documents. But for visa and documents issues, I turned to special agents about which you can get more info here.