Fix link.

README.md

 * [Mautic](https://github.com/mautic/mautic) - Email marketing automation
 * [PHPMailer](https://github.com/PHPMailer/PHPMailer) - Another mailer solution.
 * [PHP IMAP](https://github.com/barbushin/php-imap) - A library to access mailboxes via POP3, IMAP and NNTP.
-* [Stampie](https://github.com/Stampie/Stampie) - A library for email services such as [SendGrid](https://sendgrid.com/), [PostMark](https://postmarkapp.com), [MailGun](https://www.mailgun.com/) and [Mandrill](https://mailchimp.com/en-gb/features/transactional-email/).
+* [Stampie](https://github.com/Stampie/Stampie) - A library for email services such as [SendGrid](https://sendgrid.com/), [PostMark](https://postmarkapp.com), [MailGun](https://www.mailgun.com/) and [MailChimp](https://mailchimp.com/features/transactional-email/).
 * [SwiftMailer](https://swiftmailer.symfony.com) - A mailer solution.
 * [Symfony Mailer](https://github.com/symfony/mailer) - A powerful library for creating and sending emails.