As you may already know, Mandrill changed radically some time ago, now you need to have a paid subscription on Mailchimp to be able use the transactional message delivery service a.k.a. Mandrill, and you will need to pay for that component as well, so it can be complex and at the same time a bit expensive when you don’t need the Mailchimp features.
I know! Mandrill is great and it was really sad when we could not use the service. However, we then found SendGrid (https://sendgrid.com), it seems a bit plainer than Mailchimp, but it is a good tool for the price:
Particularly what I like the most is that you can track your messages: When was the message sent? Was the message delivered correctly? Was it open by the recipient? You can check that out from your SendGrid account. Of course, you could configure and SMTP service like Gmail or your website but SendGrid (and Mailchimp) have those features that make you love it
There is the Sendgrid WordPress plugin and a Sendgrid Drupal module that helps you integrate the service with your website.
So give it a try, create an account and you can start your free 30-day trial. Tell us if you like SendGrid more than Mandrill or if you have another favorite email service plugin.