Document information

Document ID: 4641
Subject: Cyclic connections and how to avoid them
Creation date: 12/14/15 4:35 PM
Last modified on: 8/15/18 10:35 AM

Cyclic connections and how to avoid them

A cyclic connection is created when two SMTP servers send messages to each other creating a loop. Consider the following scenario that creates a cyclic connection.

  • The IP address of your machine is
  • You are using SMTP Proxy server on port 25.
  • Traffic coming in for this Proxy server is being forwarded to port 2500 on the same machine to another SMTP server, such as Microsoft Exchange.
  • You have configured a smart host in Exchange server that sends message back to port 25 on the same machine.
  • When any user wants to send an out-bound email, either to Xeams or Exchange, it creates a loop - this means the message will continuously go back and forth between Xeams and Exchange.

Avoiding cyclic connections

To avoid cyclic connections Xeams runs an internal watchdog service that checks if messages are coming back from the host that the target for SMTP proxy server. If two cyclic connections are detected, Xeams will automatically stop the SMTP Proxy server and then restart it later on.

Log files

When a cyclic connection is detected, Xeams will log the following message in Xeams.log file:

Staging server is enabled and received a message from the same host where proxy server forwards the message. This could be a cyclic message.

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