@numarc: Don't use the mod at the top of page 1. Use the mod that is linked to on the bottom of page 1.
but for those people with bigger boards, why isn't this a real problem? Suppose you have a thread that more than 100 users have replied to...whenever someone posts in that thread an email is supposed to be sent to more than 100 people -- why doesn't that create the ISP problem that this mod fixes for mass emails?
It does create the problem. I never argued that. I only said, this mod (as it is) won't fix it. You could apply the method, however it won't be IMHO very userfriendly. If anybody wants to do it, though, go ahaed. But please in a different thread, since it is a different mod.
Also, one question about the mod: does this mod also make it less likely that a mass email will be treated as spam (even for mass emails to less than 100 users), since the TO field gets filled in so that the email is no longer to an undisclosed recipient?
The TO: Field is already being filled with a valid email adress by the default phpBB installation. No change in that.