Since hashtags cant really do much when they are in an email subject line,
and they seem to sometimes add in the same tag multiple times to subject lines
with multiple email replies -
perhaps the option to remove them from any email subject could be an option
at the owner level, or maybe let it be an option in the users subscription settings.
After all, they are not relevent at an email level... at least with my group they
are not. But for purposes of navigation on the web interface to see what kind
of subjects are popular, they are of good value as long as the owner or mods
are vigilant and group them together accordingly on a regular basis... which is a great help
when a potential new user wishes to join, and can review what the most popular tags are.
Another option could be to let the user subscribe to only certain subject tags and not others.