Cisco Cisco Email Security Appliance X1050 Troubleshooting Guide
Email Security Appliance Round−Robins to the
Next SMTP Route If a Destination Mail Server is
Still Responsive
Next SMTP Route If a Destination Mail Server is
Still Responsive
Document ID: 117875
Contributed by Enrico Werner, Cisco TAC Engineer.
Jul 08, 2014
Jul 08, 2014
Contents
Introduction
Background Information
Problem
Solution
Example Scenario
SMTP Routes
ESA Mail Log
Background Information
Problem
Solution
Example Scenario
SMTP Routes
ESA Mail Log
Introduction
This document describes how the Email Security Appliance (ESA) behaves when a destination host
configured in the SMTP routes responds with a 4.x.x SMTP code.
configured in the SMTP routes responds with a 4.x.x SMTP code.
Background Information
Simple Mail Transfer Protocol (SMTP) routes allow you to redirect email that is specified for one domain to a
different mail exchange (MX) host. A domain that receives email can have multiple destination hosts, each
assigned a priority number, similar to an MX record. Destinations with identical priorities are treated in a
'round−robin' fashion where if one or more of the destination hosts does not respond, the messages are
delivered to the next functional host.
different mail exchange (MX) host. A domain that receives email can have multiple destination hosts, each
assigned a priority number, similar to an MX record. Destinations with identical priorities are treated in a
'round−robin' fashion where if one or more of the destination hosts does not respond, the messages are
delivered to the next functional host.
Problem
A functional exchange server destination host can respond with a 4.x.x SMTP response that indicates the
server cannot accept email due to insufficent system resources. Here is an example of a 4.3.1 insufficent
system resource message:
server cannot accept email due to insufficent system resources. Here is an example of a 4.3.1 insufficent
system resource message:
4.3.1 − Mail system full ('452', [4.3.1 Insufficent system resources'])
Solution
If a destination host responds with a 4.x.x SMTP response code, no action is required. The ESA automatically
acts on the response and delivers the message to the next configured destination host in 'round−robin' fashion.
acts on the response and delivers the message to the next configured destination host in 'round−robin' fashion.
Example Scenario