I have used mailchimp and its API mandrill in couple of projects recently.
Both of these projects had requirements to send a relatively complex emails such as confirmations to customers, detailed invoice and account totals which required a strong email template engine to allow sending object list and let the template itself loop through the objects and display them.
I found Mandrill and their template engine which you can set it to use Handlebars.js is very powerful and fit my needs pretty well.
Because Mailchimp templates design editor is robust and easy to use, we started to build the templates in mailchimp then pushed to mandrill to be called from my project.
Till this moment everything looks perfect and no problems.
But, what happened next is the following:
I wanted to remove some code which Mailchimp template designer adds to the template by default: https://stackoverflow.com/a/46185879/20126
So I went to the Mandrill template editor, (which has no UI, you will need to update pure HTML) and updated the code there. all good, But now I can’t push the template back to Mailchimp, there is no way to sync between them anymore, and as a result I have now 2 different version of the same template, original one on Mailchimp (which I don’t to push anymore to Mandrill), the Mandrill new updated version.
And the real pain behind this that the Mandrill email template editor is very poor comparing the rich design Mailchimp template editor.
Mailchimp: please you will need more integration functions with Mandrill to look like one application.