We're in the process of implementing a new ASA moving from an old SonicWall 3060. When we put the new ASA in place we're having some issues with email, specifically verification via MX Toolbox. When in place, MXToolbox is showing SMTP reverse DNS error, no TLS support and SMTP transaction time delay notifications. When we roll-back to the SonicWall these issues disappear. I have verified ESMTP is disabled, yet we are still experiencing issues. It appears we are receiving these errors because the connection is timing out. Is there another inspection policy or parameter that needs to be disabled?
