README

Because bitbucket says:

U.S. law prohibits Atlassian, an Australian corporation with offices in the United States, from providing access to our products and services to organizations or End Users located in the following countries and regions; Crimea Region of Ukraine, Cuba, Iran, North Korea, Syria, Sudan.
Atlassian can no longer allow users from the above countries to use or access our products or services. Accordingly, you will no longer be able to log in to any of our hosted solutions, including Bitbucket.
Sincerely,
Atlassian

and mandrill-api-php official hosted in bitbucket, we create a mirror to access it via packagist.