Many people wonder, if the definition of Spam is based in bulk, just what it means and how people can detect it in E-mail, when they only get one copy themselves. Defining Bulk Bulk E-mail is, in for the purposes of defining Spam, the use of automation to send the same message to multiple unrelated parties. These terms themselves need refining.
Automation means using computers to make it much easier to send the same message to lots of people.
It doesn't just mean a traditional mailing list or bulk mailing program. Writing any letter where you use a computer to insert the a significant part of the letter with text also sent to others is bulk mail. Having a computer prepare a raft of subtly different messages that mean the same thing is still automation. As noted, variants of a form letter are the same message. Unrelated parties are people that have no personal knowledge of one another.