Mandrill Changes, Requires MailChimp
In short, Mandrill will no longer be a separate product. It will be dedicated as a paid addon to Mailchimp and will require a Mailchimp account in order to be used.
Mandrill users have until the 16th of March 2016 to create their Mandrill accounts or find another service.
Read the announcement: Important Changes to Mandrill
Which Way To Go?
This can be both good and bad for MailChimp, it all depends on the details of this announcement.
So many users use Mandrill with 3rd party applications including integrations such as sending emails through WordPress, directly from their servers, etc. If these 3rd party integrations are cut off completely, it may be problematic for MailChimp in my personal opinion.
If the announcement specifically refers to the merging of the two services and that a MailChimp account will be required but that the Mandrill API will still be available to be used then the story is different.
If you want to move over to a different service, here are the best alternatives:
See our SMTP Relay Services documentation for instructions on setting up with our WordPress Newsletter plugin.
Some additional SMTP/API relay providers recommended by our users: