Hello, We have also encountered this issue sporadically with our Docker-based Mailman installation (maxking/mailman-web and maxking/mailman-core 0.5.2).
Here are excerpts from the email sent to the LIST-request address: (sent by Outlook/Exchange)
Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 MIME-Version: 1.0
DQo= <<<
And here is the response:
Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 MIME-Version: 1.0
Difvv73vv70H77+977+9Kyx477+9a3rvv70gailK77+9ae+/ve+/ve+/vSzvv73vv73vv716e++/ ve+/ve+/vdqeB++/vXooLQ0K77+9Wu+/vVsdeu+/vSvvv70I77+9alfvv70177+9Ie+/vSch77+9 WicaV++/ve+/vd2t77+9Andree+/vQbvv73orJdo77+9DQo=
This does not appear to be base64-encoded UTF-8.
Does anyone have any idea how to fix this? Best regards, Frank