Either don t send attachments or make sure your recipient is able to handle the attachment in the form that you are sending. There are several converters so most current word processors are able to read documents created in other word processors. There is additional work that must be done to install these converters as part of your word processor. Yes, in two ways. OWA is a more reliable feature rich way to access e-mail from off campus.
Protocols are the languages that are spoken over the network and Internet.
There are several protocols for different services. IMAP accesses your e-mail from the server but keeps the message on the server. With IMAP you can access all of your e-mail from for example home and work with the same client software on both.