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Why is the message log of my Email Security Gateway reporting sender timeouts after successful delivery of messages from Google and other specific email providers?

  • Type: Knowledgebase
  • Date changed: 3 years ago
Solution #00003210

All Barracuda Spam Firewalls, all firmware versions.

Recently, some large mail providers have been making changes to their mail servers that cause Barracuda Spam Firewalls to report sender timeouts in the message log. With these changes, sending email servers are leaving SMTP connections open for some time - typically thirty (30) seconds - after delivering a message before sending a QUIT.

It is believed that these changes may ultimately improve the global efficiencies for sending email servers in delivering subsequent messages because keeping connections open is significantly less expensive from a resource perspective than opening new ones. This behavior has been reported by Barracuda Spam Firewall customers receiving email from Google, Comcast, and Road Runner email servers among others.

While the behavior of leaving outbound SMTP connections open may be more efficient for the sender at a global level, the open connections also consume resources for handling inbound connections on the Barracuda Spam Firewall. As such, to prevent unnecessary resource usage, the Barracuda Spam Firewall has a parameter for tuning incoming SMTP timeouts to minimize resource utilization when misbehaved email servers or stateful packet inspection firewalls do not properly close SMTP connections.

The marker of this behavior is typically a successful email delivery followed by a log entry for a sender timeout. This timeout is simply reporting that the Barracuda Spam Firewall closed the open connection after the successful delivery of the message and hit its incoming SMTP timeout value prior to receiving a QUIT command from the sending email server.

Important notes:
  1. No email is lost as the result of the Barracuda Spam Firewall closing this connection before the final QUIT command.
  2. If you would prefer to wait for the sending email server to send the SMTP QUIT command before dropping incoming connections, you can increase the Incoming SMTP timeout value in the Advanced -> Email Protocol screen under SMTP Configuration. The default value is 30 seconds.
For receiving email from Google servers, you can increase the value to 45 seconds.

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