For receiving email, why would you want to donate your bandwidth costs to spammers? I understand the desire to use Postfix though, so just use Gmail, or even Pobox (which has adjustable spam settings), then forward to your own server with some whitelisting in place. Then at least you've cut your bandwidth by about 99%.

For sending email, there are some steps for DNS and signing missing here that can result in your email going to spam with the major ISPs. It looks like he was going to add Domain Keys in v6 but abandoned it.