A rule like the one above is potentially very dangerous because an error in the pathname there will eat up all incoming mail that was not picked up by an earlier rule. Use grab and drop to prevent typos and check your rules before you leave them in place. Expect the worst, test your rules carefully, and once you have a working rule, don't fuss with it. MAIL A mail filter separates the mail you want from the mail you'd rather not see, and discards the latter automatically. A mail filter is potentially dangerous because there is always a chance you may end up discarding something you didn't mean to discard.
Some spam is likely to elude the filter.
This is annoying, but it's not as bad as having legitimate mail get picked up by the filter. To avoid the possibility of losing legitimate mail due to a mail filter, you are advised to route the discarded mail to a mail folder where you can review it before you finally discard it. This means you won't have a fully automated filter, but it is a safety measure that is probably worth the extra work. Then you can periodically scan this folder and see if anything legitimate landed in there by accident. But if you are truly convinced that you want to set up a filter rule without the saftey check, you can kill incoming mail by trapping it with a rule that routes it to a non-existent directory.