What I ended up doing last night was using a code step to run Nodemailer to send via my Fastmail account. But that’s awkward and doesn’t act like a true email forward (I’m manually preserving the Date and Message-ID headers, but nothing else, and if I did want to try and preserve all headers, it wouldn’t be attaching the new headers that are intended to be provided when forwarding messages). Thankfully for my particular use-case that doesn’t really matter, but I wish there was an easier way to do this.