I can confirm the outdated release image from another change in mail-receiver.
I opened this PR, which was merged on 11 August: FIX: Use email_encoded for incoming mail - Pull Request #37 - discourse/mail-receiver - GitHub
It changes the mail receiver from:
post.set_form_data(email: @mail)
to the newer email_encoded parameter expected by Discourse.
After the PR was merged, I rebuilt mail-receiver on 17 August, but the freshly rebuilt container still contained:
post.set_form_data(email: @mail)
I added the details to the merged PR here:
I rebuilt again on 22 August and ./launcher rebuild mail-receiver reported the published release image as up to date, with digest:
sha256:2a0d45bb92a783c846a821e635413764eeadb3441ef6190085545a4bf054cb1e
Incoming mail still works on my installation, but each received email continues to trigger Discourse’s:
the email parameter is deprecated
warning because the published image does not contain the merged #37 change.
So this appears to independently confirm the first issue you’ve found: changes merged into the mail-receiver repository have not been making it into the published discourse/mail-receiver:release image.