That wouldn't be all that effective. with 10 posts plus one new topic, it
would only take 10 new accounts to flood the forum with 110 spam posts, some
of them within existing topics and some of them as new topics. That's why I
think making them approval-only at first would be best. There could be a
notice saying that new accounts need their posts approved until X posts are
approved and the account is at least Y days old.
It would also be useful if a new account can be flagged by a moderator as
suspicious or something and have that stop the account from gaining
free-posting status until that mark is removed. So if an account is making
several posts in a short period of time that aren't spam or against the
rules, but aren't really contributing to the discussion, that mark could be
applied to the account and the user could be notified as to why. Then it
would be up to that user to earn the trust of the moderators, presumably by
consistently posting things that are not spam.
If the minimum post requirement is small enough (say, 15 or 20), it wouldn't
be a particular burden (you would get that number of posts approved quickly
if you're a semi-active user, and then it would just be a matter of waiting a
short period for free posting status to be granted), and yet it would make
spamming a lot too complex to be practical (having to create an account, make
posts that aren't spam and aren't suspicious, and then wait for however long
the wait period is, and then when you're done, having all your spam posts and
your account deleted in the blink of an eye).
