Sendmail: How does one blacklist annoying spammers?

[Daniel B. Thurman]

I thought it was sufficient to look into the headers
of the offending email spammmers and add these respective
IP address and/or host names to the /etc/mail/access file,
but I am beginning to suspect that these headers could be
easily spoofed with bogus entries, right?

I am really getting tired of adding in entries into the access
file, and writing email filters (in thunderbird) for patterns
dumping spammers into the trash - and yet - I am still forced
to review the trash for entries that should not have been trashed.  
Seems like a real chore and a losing proposition...

What do admins of sendmail use, besides spamassasin?

Thanks!
Dan