Cisco Cisco Web Security Appliance S670 User Guide

You can configure one or more SMTP relay hosts. When you configure multiple SMTP relay hosts, 
AsyncOS uses the topmost available SMTP relay host. If an SMTP relay host is unavailable, it tries to 
use the one below it in the list.

Choose Network > Internal SMTP Relay. 

Click Edit Settings.

Complete the Internal SMTP Relay settings.

(Optional) Click Add Row to add additional SMTP relay hosts.

Submit and commit your changes.

AsyncOS for Web can use the Internet root DNS servers or your own DNS servers. When using the 
Internet root servers, you can specify alternate servers to use for specific domains. Since an alternate 
DNS server applies to a single domain, it must be authoritative (provide definitive DNS records) for that 
domain. 

AsyncOS supports split DNS where internal servers are configured for specific domains and external or 
root DNS servers are configured for other domains. If you are using your own internal server, you can 
also specify exception domains and associated DNS servers.

Relay Hostname or IP 
Address

The hostname or IP address to use for the SMTP relay

Port

The port for connecting to the SMTP relay. If this property is left empty, the 
appliance uses port 25. 

Routing Table to Use 
for SMTP

The routing table associated with an appliance network interface, either 
Management or Data, to use for connecting to the SMTP relay. Choose 
whichever interface is on the same network as the relay system.