According to my records, it seems that on August 4th or August 5th, the API returns null for plain_content when I try to retrieve an Email using REST /emails/{id}. It use to return a Base64 encoded plain text where it contains a public url that would display how an email that was sent to the recipient looked like.
We really depended on this. Is there a reason why this was removed? Is there another way of getting the public url? Is this a bug or are there plans on getting it put back in?