Google just added a nice new feature to Google Apps accounts, allowing users to authenticate emails by signing them with DomainKeys Identified Mail (DKIM). Big words, but basically it means your email's considerably less likely to be marked as spam.
Straight from the Google Enterprise blog:
Today, we mark another notch in the spam-fighting belt: we're making it possible for all Google Apps customers to sign their outgoing messages with DKIM, so their sent mail is less likely to get caught up in recipients' spam filters. Google Apps is the first major email platform – including on-premises providers – to offer simple DKIM signing at no extra cost. Once again, the power of the cloud has made it possible for us to bring this feature to millions of customers quickly and affordably.
Enabling it is pretty simple. Log into your Google Apps account (normally you can just point your browser to http://google.com/a/yourdomain.com), then click the Advanced tools tab and click the Set up email authentication (DKIM) link at the bottom of the page. Then generate a new DNS record.
From here it's a little trickier to detail, since creating new DNS records varies depending on your domain host. Essentially you need to create a new DNS TXT record with google._domainkey as the TXT name and a long string that's essentially your DKIM key as the TXT record value. You then save the new DNS record, and click the Start authentication button at Google Apps. It can take some time for your DNS records to propagate, but once they do, your Gmail account should start signing your messages.
Note: My personal domain is hosted by Dreamhost, which doesn't seem to like the underscore in google._domainkey and is preventing me from creating the new TXT record. Other Dreamhost users having similar problems? Got a solution? I'm all ears.
Spam takes another hit: email authentication now available to millions of Google Apps customers [Google Enterprise Blog]