Using: movemail (GNU Mailutils) 3.9
mailutils: stable 3.9 for macOS 10.15.5 via github.com/Homebrew/homebrew-core/blob/HEAD/Formula/mailutils.rb Retrieving message (via imaps to dovecot server) with header (main or nested): Content-Type: ... boundary="whatever" when retrieved and placed into mbox becomes Content-Type: ... boundary=whatever So it appears that movemail is removing the quotes on a quoted boundary string. This can cause decoding of messages to fail. For example, in Emacs 26.3 RMAIL decode fails if the boundary string contains an equal sign; boundary=...=... confuses the decoder, whereas with quotes intact boundary="...=..." produces correct decoding of mime components with no error.
