For example, https://mail.python.org/archives/list/python-ideas@python.org/message/NAH2RR...

As I received it, some lines actually exceeded the SMTP hard limit of 998 characters (excluding the separating CRLF).

There are several alternative approaches; I think the best is to leave the logical lines alone, and break the physical lines with format=flowed.

Issue #341 filed. https://gitlab.com/mailman/hyperkitty/-/issues/341