Problem

-- Under Connection tracking, a lot of connections from Postini servers are shown as failed due to SMTP error.

-- Mail is flowing normally without any issues

-- Postini is used in front of MailGate

Resolution

The errors can be safely ignored. As Postini servers use recipient verification algorithm known as "Next hop recipient check", every session from Internet to Postini for the company domain(s) is mirrored to next relay (in this case MailGate) and next relay response is sent back to external sender. So after the DATA command is sent by the sender, the session between Postini and Mailgate is closed. Mailgate assumes this session as failed since no message is received.