Spam refers to the same thing over and over again. It originally applied to massively cross-posted Usenet articles, but has been expanded to include most forms of net abuse. The term spam comes from a skit by Monty Python's Flying Circus . There are many ways to get on the spammer's mailing lists. Some are as simple as choosing an unfortunate e-mail address, some are not so simple.
Many people sign up for mailing lists on subjects that they are interested in.
Unscrupulous people will also sign up on mailing lists in order to obtain e-mail addresses. If an e-mail address is used by someone on one ISP , it is fairly certain than someone else has used that address at some point. This is particularly true for common words and names. Spammers will use the front part of the e-mail address and change the ISP name to all the other major IPSs. Leave all the other fields blank.