Do any you have any ideas of what offline email mean? How could you use email offline?

It could be in a LAN/WAN. Provided you have a network you can send internal emails, no problem.

Another thought, you might wish to create your emails while offline then go online to send and receive - this is more when you hae a dial-up service which is charging by the minute. If you are composing a lengthy email it could be costly to be online while you type.