Electronic mail (e-mail) and anything corresponding to use of the Internet uses a combination of electromagnetic waves (light) and electrical signals. For instance, if you send an e-mail the information you typed in your e-mail is read and broken up into different size 'packets' of information. These packets are totaled and given the unit of bytes.

Longer e-mails have more packets and more bytes than shorter e-mails. The packets are then sent to a 'router' at your Internet service provider (ISP) This router will then send the information to another router which will send to another and so on until it reaches its final destination (the e-mail address you provided for sending thee-mail). (You can think of a router like a post office).

All this information is sent through cables. Some cables send electrical signals and other send optical(electromagnetic signals).

There are large bundles of fiber optic cables on the bottom of the ocean for information to be sent overseas (optical signals) and then there is some converter for these signals into electrical signals (read by your computer).

If you are interested learning more about the Internet and e-mail I would suggest visiting: computers