Cannot block certain emails with blacklist

I have several emails that arrive every day, sometimes several times per day. I have tried many times to blacklist the sending address inside Squirrelmail. They always show the same sending address, yet this blacklisting doesn’t work.

I know how many times spammers change their sending addresses, but these all seem to come from the same address every day - but even though I have it blacklisted, it comes thru.

Any suggestions?