Add improvmx (#2277)

README.md

@@ -235,6 +235,7 @@ API | Description | Auth | HTTPS | CORS |
 | [Freelancer](https://developers.freelancer.com) | Hire freelancers to get work done | `OAuth` | Yes | Unknown |
 | [Gmail](https://developers.google.com/gmail/api/) | Flexible, RESTful access to the user's inbox | `OAuth` | Yes | Unknown |
 | [Google Analytics](https://developers.google.com/analytics/) | Collect, configure and analyze your data to reach the right audience | `OAuth` | Yes | Unknown |
+| [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 |
 | [mailgun](https://www.mailgun.com/) | Email Service | `apiKey` | Yes | Unknown |