In form settings you can use many types of form. Many email marketing tools are available in this form. Like that database, Wp-mail, FeedBurner, MailChimp, Aweber, Campaign Monitor, Constant Contact, Mad Mimi and Get Response. You can use all tools very easy integration. You no need any code you can simply paste your username and API key then will connect automatically. You can see your subscriber and send mail.You can use below these tools.
Go to -> Notification Settings -> Form Settings
- Feed Burner
- Campaign Monitor
- Constant Contact
- Mad Mimi