Reply by email stops working

I have reply-by-email set up working back in June with the mail receiver docker container. I’m not sure what has happened (I haven’t done any upgrade since), but the server can no longer process incoming emails.

Mail receiver log:

<23>Sep 16 05:47:49 receive-mail[5333]: Recipient: replies+de9850e89875889b6f8c13d7a9de6d18@url-redacted

<19>Sep 16 05:47:50 receive-mail[5333]: Failed to POST the e-mail to https://<url redacted>/admin/email/handle_mail: 400

Discourse log

Started POST "/admin/email/handle_mail" for at 2021-09-16 08:14:36 +0
ActionController::BadRequest (Invalid request parameters: Invalid encoding for parameter: Received: from MTA-11-3.url-redacted (mta-11-3.
        by discourse-ubuntu-nyc1-mail-receiver.localdomain (Postfix) with ESMTPS id B234513F82C
        for <replies+de9850e89875889b6f8c13d7a9de6d18@<url-redacted>>; Thu, 16 Sep 2021 05:47:49 +0000 (UTC)

Perhaps your mail receiver or discourse is out of date? Perhaps the API key is invalid? I would first try to

cd /var/discourse
./launcher rebuild mail-receiver

Is it all incoming mail or just some with a bizarren encoding?