I have troubles with spam being blocked by sendmail and/or SpamAssassin.
I receive some 70+ spam messages a day and I really like them filtered out, I have installed SpamAssassin and it does a great job. BUT some mails (which are spam) gets blocked and sent back to the spammer and my ISP isn't happy about me sending them back. My ISP recognizes those rejected mails as spam and blocks ME from sending legitimate mail

How can I make my sendmail/SpamAssassin installation stop rejecting spam and simply mark them as spam and deliver them to the mailbox (where I can filter and delete them)

Thanks in advance