Unsolicited Bulk Email ("spam")
The sending of Unsolicited Bulk Email (UBE, colloquially known as "spam") has become a major nuisance. Informative reading on the topic may be found at, for example, http://www.cauce.org/.
In the scope of these notes, we can do no more than scratch at the surface of the topic, but at least we want to make some suggestions to users about appropriate behavior in response to spam, and explain a little about how the departmental mailer attempts to deal with the problem.
This section discusses the general issue. To find out more about what happens in the departmental mailer, see Departmental Email server policy and operations.
"Spammers" get their lists of millions of email addresses from all manner of sources: by trawling web pages, by buying address lists from unscrupulous providers of email accounts, and so forth. Some of them also send their unsolicited mails to inadequately-managed mailing lists.
Initially, the email addresses which are harvested for spamming are considered to be unconfirmed: they might or might not represent a valid email address which gets read by a human recipient. But "thanks" to the minimal cost of operating a mail server, they blanket-mail all the addresses which they can get their hands on, whether valid or not.
If, however, they can succeed in getting a human response to one of their missives, whether to complain about the unwanted nuisance, or to naively request them to stop, then they can mark that address as "confirmed" and it in turn becomes a more-valuable commodity which they can sell (i.e in the form of a list of confirmed email addresses) to other spammers.
The cost of sending out these vast numbers of emails is so tiny that if even a miniscule fraction of the recipients is duped into purchasing whatever product or service is being advertised, they get their profit. But meantime they have stolen the computer resources to distribute the mail, and the time and effort of unwilling recipients in inspecting and dealing with it, from all of the other targets of their abuse.
As is explained in more detail under Departmental Email server policy and operations, we implement a series of precautions against accepting spam, consistent with avoiding unwanted interference with bona fide emails. Nevertheless, it must be understood that a certain amount of spam WILL still get through. By applying rather more-aggressive rules, we could reject quite a proportion of the spam which still gets through to our users, but only at the risk of rejecting significant amounts of bona fide email too.
We of course also take precautions to avoid our mail server being used as a relay for distributing spam mail to others. This is an aspect which normally isn't visible to our users, but it explains the reason why those users who attempt to use our mail server in the "normal" way from their domestic Internet Service Provider find their attempts are rejected.