Your recipient's MIME compatible mail reader translates the message back into readable characters. Take a look at the following message. Eudora negotiates it automatically. We use UNIX email at Yale. There are email servers available for all platforms though, and you could run one on your desktop computer if you wanted to.
Most library staff have POP-only accounts.
The client attaches to the server and downloads the messages to the local computer. Other first level domains include com, mil, org, net, gov. Except in the USA, first level domains are usually a 2 letter country code. The easiest way is to ask. If they work for a university or large company, try the institution's home page.