Official migration data is often outdated and inconsistent and data formats used by different nations can be incompatible, researchers at the Max Planck Institute for Demographic Research in Rostock, Germany, said.
Official records are difficult to use, as emigrants tend not to register after they move to a new country or do so very late, they said.
"Global internet data does not have these drawbacks," researcher Emilio Zagheni said. "You are where you e-mail."
Zagheni, along with Ingmar Weber from Yahoo! Research, traced e-mails sent by 43 million anonymous Yahoo! account holders between September 2009 and June 2011.
They were able to infer the residence of the senders to at least the country level by the sender's IP address.
When a person started sending e-mail from a new location permanently, it was assumed that he or she had changed residence, researchers said, allowing them to calculate rates of migration from and to almost every country in the world.
Only anonymous data was used, so identifying individuals was impossible and no information about the recipients, the subject, or content of a message was accessed, researchers said.
"What we addressed so far is only the tip of the iceberg," Zagheni said.
Digital records can give demographers a more accurate picture of population dynamics in regions they can so far only guess about, he said.
"This research has the most potential in developing countries, where the Internet spreads much faster than registration programs develop."