I have a customer that is having issues sending emails to a few recipents. The have an SBS 2003 server running Exchange. The error they are getting is the following, 554 Transaction Failed Spam Message not queued.
Thier MX record is pointing to Google Apps (Free Version) and the Exchange Server POPs the emails into the respective Exchange mailbox. Outgoing emails goes directly out from thier Exchange Server to the recipient. They are getting the error above with about 2-3 recipients on different domains. I have checked the rDNS and it resolves correctly (Exchange Server External IP = dns name) DNS name however does not match the inbound MX records as those records are the Gmail MX records. I don't believe this could be the cause as I have other customers using this same configuration and haven't had any complaints from them.