I built this Add On in order to have an option on the market for email campaigns natively inside of Gmail. I wanted to eliminate the complexity of the some of the email campaign add ons out there (where you have to interact with a separate interface, or have an account with a certain CRM). None of that with Tickle Mailer. It's lightweight, and looks at your Google Contacts. Select the recipients by choosing the Google Contact label, then schedule your emails. Spintax, Merge fields, inline images and attachments supported.
Tickle Mailer