What is the difference between Wi-Fi and cellular data?

Does email use data or Wi-Fi?

Mobile Email is considered data usage, therefore it will use up data from your data package. Megabyte usage depends on several things such as how long you are using the mobile email app and how large the email received and sent are so it would hard to determine how fast that data usage would add up.

How does Wi-Fi work with mobile data?

For example, suppose that a piece of mobile data is generated by a user typing on a device keyboard or touch screen. A Wi-Fi connection sends that individual piece of mobile data from one device to another through a complicated network of cell towers, IP connected stations and other types of network architecture.