Email Delivery Failure Scenarios

Products

• Email Security.cloud

Issue/Introduction

This is an explanation for the email that goes in retry or failed delivery.

Environment

Email Security.cloud

Cause

If we are unable to connect to the recipient mail server, i.e. a connection times out or is refused, we immediately fail over to the next route that we have for the recipient domain. If there are no more routes, the mail is queued for delivery at a later time.

If we are able to connect to the mail server and receive a 4xx temporary error, we queue the mail and attempt to deliver it at a later time to the same server.
If we are able to connect to the mail server and receive a 5xx permanent error, we bounce the mail back to the sender.

Resolution

Emails only go into retry and queue in the following circumstances:

• The recipient mail server generates a temporary (400 series) error when Symantec.cloud attempts to connect. We then queue the email and retry the connection until the server accepts it or the retry period expires.
• The recipient mail server does not respond at all. If we get no response, we queue the email.

Emails do not queue in the following circumstances:

• The recipient mail server generates a permanent (500 series) error when Symantec.cloud attempts to connect. This causes the email to immediately fail and bounce back to the sender.
• The recipient mail server responds and accepts the email into the network. The email is then delivered or queued within the recipient network.