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In general, no. While SpamAssassin is very good at picking out a large proportion of spam, it's impossible for a computer to do this job perfectly. You should only delete mail if you (and your users/customers) would find it acceptable to lose mail that might be legitimate. A much better idea is to filter possible spam into a separate folder that can be checked less frequently than the normal mailbox. It is possible to reject the mail at the smtp level, generating a delivery error, so the sender is notified that their message is rejected. This works well imo. You need to use a mail server that supports this(I use mimedefang+sendmail). Mimedefang also allows me to save the mail to a central archive that I can extract from if I get a FP. If you do reject mail at the 5xx delivery level you need to set your spam threshold higher than the default of 5.

If you have so much spam that manually reviewing all messages isn't practical, you can reduce the damage by creating rules to implement a whitelist. You can also implement through rules an "email password"; email that includes the email password in the subject (or body) could be ranked as much less likely to be spam. Then, make sure that those who might legitimately contact you can learn the email password, e.g., placing a shrouded graphic of the email password on your website. Make sure you can can change your email password later (e.g., by changing rules), in case spammers start including your old email password. You can see more about email passwords at http://www.dwheeler.com/essays/spam-email-password.html

(EditHint: I log in into a shell account, so I wrote a perl script that checks my spam mailbox for new messages \[i.e. those missing a Status field in the header\] and included it in my .bashrc.  This script, with the -r option, also marks all those messages as read so I don't see those same headers popping up next time I log in.)

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