Dave Plowman wrote:

Can you explain? Most reply to an email if needed. So what on earth is
follow up?

As you're not a thunderbird user, you might not appreciate that by
default it has multiple buttons in multiple toolbars, reply, reply-all
and forward are pretty normal across all mail/news clients, but
thunderbird seems to think it's necessary to have a follow-up button as
well, it seems to confuse people into sending direct email replies to
the O/P, rather than replying to the group, I've always hidden the extra
toolbar ...