I've just spent a frustrating hour with Google support and have nothing to show for it.
We host an Exchange 2010 server, and send email directly, not via a smarthost.
Our static IP has a PTR record which matches the MX Record which also matches the server name used for helo/ehlo. We also have a strict SPF record.
Yet any mail we send to a Google Group get's bounced as spam. Sending to a Google Apps user or Gmail address is fine, it only fails to a Google Group.
Google support say they can't tell me why it's failing as they say it would compromise the effectiveness of there spam filter if people knew why it was blocking their emails!
We are not on any blacklists and have no trouble emailing anywhere else.
Has anyone else experienced this and found a solution?