Comment (by Roland Haas):

While this is really strictly an issue with the sender’s mail client, this problem is not going away. A partial workaround is to add some css to the <pre> element that Mailman (well pipermail I guess) is using in the its html pages. Something like:

overflow-x: auto;
white-space: pre-wrap;
white-space: -moz-pre-wrap;
white-space: -pre-wrap;
white-space: -o-pre-wrap;
word-wrap: break-word;
width: 78ch;

word-wraps at the 78 character since it sizes the element to be as wide as 78 “0” characters and asks for word wrap.

Possibly this could be added to the html template used: https://wiki.list.org/DOC/4.48 How can I change the HTML or .txt templates used by my mailing lists%3F

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/723/archived-emails-to-mailing-lists-are