You are experiencing a complete failure of outbound emails sent through Symantec Email Security.cloud.

For mail that is passed from your infrastructure to Email Security.cloud

For issues that relate to messages that your mail servers pass to Email Security.cloud, check the following:

• Check that your outbound IP addresses for your email message gateway or hosted email service provider are registered in the Symantec.cloud console under Services > Email Services > Outbound routes.
• Ensure that either your firewall or mail server is set to allow SMTP connections to Symantec.cloud. See IP ranges for Symantec.cloud.
• If you continue to experience outbound connection failures, capture and save an outbound SMTP connection log from your server and any detailed (verbose) log from your server, and then contact Support to submit the log for analysis and further assistance. 

For mail that Email Security.cloud tries to deliver to a third-party recipient

For issues that relate to messages Email Security.cloud tries to deliver to a third-party recipient, check the following:

• If the recipient mail server responds with a "500" bounceback message, this is a permanent failure, and may indicate one of the following:
  • The mail server exceeded its storage allocation.
  • The mail recipient's address is not valid.
  • The mail server uses it's own filtering solution that discards the email.
• If the recipient mail server responds with a "400" bounceback message, this often indicates a temporary delay or issue in sending the message. Email Security.cloud will try to deliver the email for seven days. See Email retry schedule in Email Security.cloud for more information.
• If the recipient mail server does not respond to requests from Email Security.cloud, our service will queue the message until we receive a response, or until the email retry period expires. See Email retry schedule in Email Security.cloud for more information.