How do you stop an anti-spam filter from blocking emails that aren't spam?

Usually once you find the email you need in your spam folder, you can click on it and tell the computer "this is not spam". The next time you receive email from that address it shouldn't get dumped into your spam. Sometimes you can manually add an email address into your address book so that when it comes, it won't be spam b/c you've allowed it already. For instance, I signed up to receive emails from a department store for coupons. The frequent shopper card said add blahblahstore@blah to your email address book so I did. Now I get their emails no problem. If you have a lot of problems with it, try setting your spam blocker to a lower setting to allow more emails to come through.