The last command is resubmitting the message to Sendmail, so you are creating a mail loop. If you simply remove that last recipe, Procmail should deliver to $DEFAULT (possibly after consulting the user's $HOME/.procmailrc if present).

Oops, wait a minute, the Sendmail voodoo seems like it might be supposed to work that way, actually. Do you see anything in Sendmail's logs for stuff sent to something.procmail? Where did you get those Sendmail rules, anyway? Probably that site should have some documentation and perhaps troubleshooting tips.

(Also notice that -oi is already present in $SENDMAILFLAGS, so you should not add it explicitly. And you might want to remove those live addresses from the log file excerpt before the spammers scrape them.)