Types Of Email Marketing(Sources):

Let's briefly review the three types of email marketing:

1. Direct email

Direct email involves sending a promotional message in the form of an email. It might be an announcement of a special offer, for example. Just as you might have a list of customer or prospect postal addresses to send your promotions too, so you can collect a list of customer or prospect email addresses.

You can also rent lists of email addresses from service companies. They'll let you send your message to their own address lists. These services can usually let you target your message according to, for example, the interests or geographical location of the owners of the email address.

2. Retention email

Instead of promotional email designed only to encourage the recipient to take action (buy something, sign-up for something, etc.), you might send out retention emails.
These usually take the form of regular emails known as newsletters. A newsletter may carry promotional messages or advertisements, but will aim at developing a long-term impact on the readers. It should provide the readers with value, which means more than just sales messages. It should contain information which informs, entertains or otherwise benefits the readers.

3. Advertising in other people's emails

Instead of producing your own newsletter, you can find newsletters published by others and pay them to put your advertisement in the emails they send their subscribers. Indeed, there are many email newsletters that are created for just this purpose - to sell advertising space to others.