For transactional email I like liquid templated markdown. We render each through liquid, then send the resulting markdown in the text/plain part, and render it

For transactional email I like liquid templated markdown. We render each through liquid, then send the resulting markdown in the text/plain part, and render it with redcarpet and github's sanitizer for the text/html part. We used to downsample from HTML to plaintext with many irksome artefacts arising. These look a lot better. It does oblige a certain discipline on the part of template writers, I consider that a good thing.