Cisco Cisco Email Security Appliance C160 Mode D'Emploi
24-7
User Guide for AsyncOS 10.0 for Cisco Email Security Appliances
Chapter 24 Validating Recipients Using an SMTP Server
SMTP Call-Ahead Query Routing
Figure 24-2
LDAP Routing Query Configured for SMTP Call-Ahead:
In this query, the
{d}
represents the domain part of the recipient address, and the SMTP Call-Ahead
Server Attribute returns the values for the call-ahead servers and the port that should be used for the
query: smtp2.mydomain.com, smtp3.mydomain.com on port 9025.
query: smtp2.mydomain.com, smtp3.mydomain.com on port 9025.
Note
This example shows just one way to configure a query that enables you to use the LDAP routing query
to direct SMTP call-ahead queries to the correct SMTP servers. You are not required to use the query
string or specific LDAP attributes described in this example.
to direct SMTP call-ahead queries to the correct SMTP servers. You are not required to use the query
string or specific LDAP attributes described in this example.
SMTP Call-Ahead Query Routing
When routing an SMTP call-ahead query, AsyncOS checks for information in the following order:
1.
Checks the domain name.
2.
Checks for LDAP Routing queries.
3.
Checks for SMTP Routes.
4.
Performs a DNS Lookup (First an MX Lookup is performed, followed by an A lookup).
If there is no LDAP routing query or no SMTP Routes configured for the domain, the result of preceding
state is passed to next stage. In any case where there is no SMTP Route present, a DNS lookup is
performed.
state is passed to next stage. In any case where there is no SMTP Route present, a DNS lookup is
performed.
When you use an LDAP Routing query for an SMTP call-ahead query and you also have SMTP routes
configured, the routing behavior depends upon the values returned by the routing query.
configured, the routing behavior depends upon the values returned by the routing query.
•
If the LDAP routing query returns a single hostname without a port, the SMTP call-ahead query
applies SMTP routes. If the SMTP routes only lists the destination host as the hostname, a DNS
lookup is performed to obtain the IP address of the SMTP server.
applies SMTP routes. If the SMTP routes only lists the destination host as the hostname, a DNS
lookup is performed to obtain the IP address of the SMTP server.
•
If the LDAP routing query returns a single hostname with a port, the SMTP route is used, but the
port returned by the LDAP query is used over any ports specified in SMTP routes. If the SMTP
routes only lists the destination host as the hostname, a DNS lookup is performed to obtain the IP
address of the SMTP server.
port returned by the LDAP query is used over any ports specified in SMTP routes. If the SMTP
routes only lists the destination host as the hostname, a DNS lookup is performed to obtain the IP
address of the SMTP server.
•
If the LDAP routing query returns multiple hosts with or without ports, SMTP routes are applied,
but the ports returned by the LDAP routing query are used over those present in SMTP routes. If the
SMTP routes only lists the destination host as the hostname, a DNS lookup is performed to obtain
the IP address of the SMTP server.
but the ports returned by the LDAP routing query are used over those present in SMTP routes. If the
SMTP routes only lists the destination host as the hostname, a DNS lookup is performed to obtain
the IP address of the SMTP server.