Symantec Messaging Gateway processes an email message in the following phases:
Phase 1, SMTP connection - During the connection phase Symantec Messaging Gateway accepts connections from legitimate senders, unless a specific policy or setting requires rejection or deferral. All of the actions that are taken during this phase are based on the IP address alone. Symantec Messaging Gateway rejects connection attempts from any IP addresses that are not permitted by a Scanner's SMTP settings. For inbound connections from IP addresses that appear in IP-based bad sender groups, Symantec Messaging Gateway rejects the SMTP connection, unless a different action is configured for the group. Based on Connection Classification limits, some connections are deferred.
Phase 2, SMTP session - During the SMTP session, Symantec Messaging Gateway accepts, rejects, or defers messages on the basis of the message envelope. It also checks Connection Classification settings and SMTP settings to determine whether accepting the message exceeds the configured limits.
Phase 3, Message filtering - After the Scanner accepts a message, Symantec Messaging Gateway evaluates the message content and renders verdicts. It evaluates the message content based on applicable policies and settings, including, if required, content filtering policies. Based on the verdicts, it applies the configured actions.
See About filtering.
Phase 4, Message routing - Symantec Messaging Gateway routes messages that have not been quarantined or held for review to a mail host. The route is determined by Domains Delivery settings and the Scanner's Local Mail Delivery and Non-local Mail Delivery settings.
See About email domains.
Phase 5, Message delivery - Symantec Messaging Gateway enforces limits on the number of connections to internal mail servers. If the address binding settings are configured to specify the IP addresses that deliver email, Symantec Messaging Gateway uses the specified IP addresses.
Figure: Inbound Message Flow illustrates the inbound message flow.