Spamfire is mainly designed to filter your own email, but it can easily be used to filter someone else's email. This can come in handy if you are an executive and want your secretary to filter your email for you or if you want to filter email for someone else in your family. See also, How to Protect Your Children From Spam.
Open the Spamfire Account Preferences. You will add the other person's account as a Helper account. Click the the Add button under Incoming Mail Accounts. In the new window that appears, select Create a new account in Spamfire (not Import account from email program). Click OK.
Fill out all the settings for the other person's email account. Here are some tips for finding the right POP or IMAP settings.
If you don't already have one, add an SMTP account in the Outgoing Mail Accounts list. Here are some tips for finding the right SMTP settings.
Set up a schedule in the Spamfire Schedule Preferences so that the account will be filtered automatically.
Spamfire will now filter the other person's email account automatically. Good email will be left on the server for them to pick up in the usual way with their email program. Spam messages will be removed from the server so they don't have to see them in their email program.
If the other person has automatic mail checking turned on, they should check their mail less frequently than you filter it, or they will receive a lot of unfiltered spam. You might try filtering their email every 5 minutes and setting their email program to retrieve mail every 12 minutes. That seems to work well.
If Spamfire intercepts a good message as spam, the other person will not receive the message and will not be able to rescue it. You must rescue it from your computer. To rescue a message for a Helper account, click the message in the Spamfire Mail window and choose Resend... from the Message menu. This will send the message back to the person's email account. They will be able to pick it up the next time they check mail.
This setup is not fool-proof. It is prone to spam slippages and problems correcting false positives, but it does work reasonably well for many people.