Wikipedia defines spam as “the use of electronic messaging systems to send unsolicited bulk
messages, especially advertising, indiscriminately”. This definition reflects the experience of most
people who have been bothered by spam. Unfortunately, technical application of the definition is
- How does a system know that an email is unsolicited, and that the recipient has not in fact
given permission for it to be sent?
- Unsolicited does not necessarily mean unwanted – it is quite possible for an unsolicited email
to be welcome, e.g. an enquiry from a new customer.
- What exactly is “advertising”?
Because of this, it is unsurprising that different people have different opinions as to whether a
particular email is legitimate or spam. In fact, it is not uncommon for one person to class a message
as spam on one occasion and as a legitimate email on another. So how can a technical system deliver
the required result with a high degree of reliability?