Online Marketing is the big overall umbrella term for all types of online marketing efforts:
Search Engine Marketing
Referrers and Links
E-Mail & Newsletters
Banner Advertising
E-mail marketing is very similar to its traditional off-line marketing model: Mail shots. With e-mail marketing you need to build or acquire a list of e-mail addresses and then send them out e-mails with a special offer, notice or other message.
E-Mail marketing is closely related to, if not the same thing, as newsletters.
E-Mail marketing has become quite hi-tech - modern e-mail marketing providers can tell you what % of your recipients opened the e-mail or even clicked through from it