I subscribed to digests on Discourse instances and read my emails in plaintext. Huge for having a really usable and readable plaintext version!
However, I recently discovered that some HTML tags were present in the digests when server lacks some translations. For instance, consider the unsubscribe link from the digest, translation is here, but is not available in the French locale.
Resulting email has following content in plaintext:
<span class="translation_missing" title="translation missing: fr.user_notifications.digest.unsubscribe">Unsubscribe</span>
with the unsubscribe link reference below. I would have expected it to be something like
 is the reference of the unsubscribe link at the bottom of the email body).