Add Mailchimp (#2408)

README.md

@@ -243,6 +243,7 @@ API | Description | Auth | HTTPS | CORS |
 | [ImprovMX](https://improvmx.com/api) | API for free email forwarding service | `apiKey` | Yes | Unknown |
 | [mail.tm](https://docs.mail.tm) | Temporary Email Service | No | Yes | Yes |
 | [MailboxValidator](https://www.mailboxvalidator.com/api-email-free) | Validate email address to improve deliverability | `apiKey` | Yes | Unknown |
+| [Mailchimp](https://mailchimp.com/developer/) | Send marketing campaigns and transactional mails | `apiKey` | Yes | Unknown |
 | [mailgun](https://www.mailgun.com/) | Email Service | `apiKey` | Yes | Unknown |
 | [markerapi](http://www.markerapi.com/) | Trademark Search | No | No | Unknown |
 | [ORB Intelligence](https://api.orb-intelligence.com/docs/) | Company lookup | `apiKey` | Yes | Unknown |