I just tested with an Exchange domain and nope, the reaction email has only standard headers and a bunch of x-ms- headers that are the same as for a regular email from that domain. In particular, it has an `x-ms-publictraffictype: Email` header that regular emails also have, and the envelope content-type and inner content-types are also identical (`multipart/alternative` and `text/plain; charset="us-ascii"` / `text/html; charset="us-ascii"` respectively).