How to setup a 'welcome' email to the people that join my mailing list

In some cases you may want to send out an automated email to an customer that joins your mailing list. For example, you have a discount code you would like people to be able to use when they sign up to your mailing list.

This is known as a 'welcome' email, which is just a simply email that is sent out to someone automatically when they join your mailing list.