Official API Clients
You can view all of the Mailchimp Transactional API clients on our Developer Tools site or check out the language-specific repositories below. You can also view sample API requests and test each endpoint right in your browser using our transactional API reference docs.
Mailchimp Transactional Email has official API clients/wrappers for the following languages:
Third-Party API Wrappers
Here's a list of known Transactional API wrappers created by third parties. Contact each wrapper's developer for detailed information.
Note: Transactional Email was formerly known as Mandrill and may still be called that by third party wrappers.
http://mcapinet.codeplex.com (C#, VB)
You need to add SPF and DKIM records and verify ownership of your sending domains before you can send email through your account. Transactional Email will not send emails from unverified domains or domains without valid SPF and DKIM records, including public domains like gmail.com, yahoo.com, and more.
A message that is rejected with the reject reason unsigned indicates that the sending domain has not been properly set up, and that your account cannot send and authenticate email from that domain.