Mailman breaks format=flowed when resent using Base64 transfer encoding
When Mailman forwards messages that have been sent with format=flowed (RFC 3676) to list recipients using Base64 transfer-encoding, it breaks the format=flowed formatting. This makes what would otherwise be a really pleasant reading experience rather terrible.
Format=flowed uses "soft" line breaks to denote when the line should be flowed on to the next. These are a "Space-CR-LF" sequence at the end of a flowed line, instead of the usual "CR-LF". When this is sent to a Mailman-managed list and the message is re-transfer-encoded using Base64, Mailman replaces the "Space-CR-LF" line endings with just "LF".
This is exacerbated for mailers/users that use the UTF-8 charset, since even if that is sent using an 8-bit or quoted-printable transfer-encoding, it is always re-encoded by Mailman using Base64 and hence breaks the F=F formatting of the message, per: https://mail.python.org/pipermail/mailman-users/2008-September/063295.html