Types

Email marketing

Sending newsletters and offers to people who have agreed to hear from you.

What it is

Building a list of people who opted in, then sending useful, relevant emails.

The rules

In the UK you generally need consent to send marketing emails to individuals, with a limited "soft opt-in" for existing customers (ICO). Big inbox providers now require authentication and easy unsubscribe for bulk senders (Google, Yahoo).

Is it still worth it?

Opinion is divided. See is email marketing still working? for the debate.