InterScan™ Messaging Security Appliance (IMSA) maintains a routing table based on the domain names of recipient email addresses. IMSA then uses this routing table to route emails (with matching recipient email addresses) to specified SMTP servers using domain-based delivery. Messages destined to all other domains will be routed based on the records in the Domain Name Server (DNS).
The domains you configure for relay domain settings (for SMTP Message Rules) are different from the domains you configure for domain-based delivery settings (for Domain-Based Delivery).
Relay domains—IMSA relays email messages that are sent only to the relay domains. For example, if the relay domains list includes only one domain, "domain.com", then IMSA will relay only email messages that are sent to "domain.com".
Domain-based delivery domains—IMSA delivers email based on domain-based delivery. For example, if we include "domain.com" and the associated SMTP server 10.10.10.10 on port 25, all email messages sent to "domain.com" will be delivered to the SMTP server 10.10.10.10 using port 25.
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