Spam.
According to the Economist last week, it’s on the decline… temporarily at least, thanks to the shutting down of a bunch of servers in Russia.
Part of the rationale Mark Zuckerberg offered for Facebook Messaging when he announced it this month was that:

So why are supposedly respectable marketers like gocompare.com sending me messages I don’t recall signing up for… and then requiring a password, email address (astonishingly) my date of birth to remove my email address from their list? Why???
This comes across very badly: one very small step short of phishing.
In the (generally) looser regulatory environment for email marketing of the United States, would expose them to risk of prosecution. This is one area where the US rules are better crafted than those in Europe, where this is not against regulation – but it is firmly against best practice standards.
In practice, what I did was to hit the ‘REPORT SPAM’ button on my gmail account.
This makes my problem go away, but is only the start of their likely headache.
Increasingly, the focus of deliverability is shifting to an engagement index. Every person that hits the ‘SPAM’ button adds to the likelihood that messages from this sender will end up in the SPAM folder, not the inbox. It doesn’t make any business sense at all to keep people on a list who don’t want to hear from you. So let people leave your list in good grace: they may be more prepared to return to you at a later date when what you have to say is of interest to them again.
I wonder who broadcasts those bad boys…surely their provider should be advising them – and surely their complaints must be through the roof.
Sigh. Some people never learn.