Cisco Cisco Email Security Appliance C650 Guía Del Usuario
19-7
Cisco AsyncOS 8.0.2 for Email User Guide
Chapter 19 Validating Recipients Using an SMTP Server
SMTP Call-Ahead Query Routing
Figure 19-2
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:
Figure 19-3
SMTP Call Ahead Query Routing Workflow
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.
Checks the domain name.
Checks for LDAP Routing queries.
Checks for SMTP Routes.
Performs a DNS Lookup (First an MX Lookup is
performed, followed by an A lookup).
performed, followed by an A lookup).