SMTP Proxy

The SMTP proxy provides a minimum of filtering on inbound SMTP mail traffic and does not handle outbound SMTP mail well. Although, it can provide some control over inbound mail with respect to requests for relaying services.

You can, however, consider it to be a first-line of defense against mail spam. Its filtering is restricted to information that is either obtained from the client host or the DNS.

The SMTP configuration can be configured to restrict relaying of inbound mail on a per-rule basis in the configuration editor by specifying a RELAY flag on a rule, all inbound mail is accepted even if a recipient address specifies relaying the absence of the flag (or specifying NO_RELAY) causes the inbound recipients to be checked against a list of allowed relay servers; the default for this list is simply the server of the routing-mode Screen whereon the proxy is running.

Managing the list of allowed relay servers, uses the following command:

edit> mail_relay parameters...

Allowed servers are maintained in a list of unnamed items that can be added, deleted, and listed.

Managing the list of spam servers, uses the following command:

edit> mail_spam parameters...

spam servers are maintained in a list of unnamed items that can be added, deleted, and listed.

Currently, there is no way to create Screen-specific versions of these data items.

SMTP Mail Handling

Mail is relayed from any source address specified in the source of a rule to the first destination in the rule that accepts the connection. The order for contacting actual inside SMTP servers (for destinations with multiple addresses) is IP-numerical order (lowest-numbered host first). If more precise ordering is needed, create multiple rules.

SMTP Proxy Filtering

When the relay flag is not set on a rule, each recipient mailbox name is checked against a list of allowed servers on which to perform relaying of inbound mail server name matching.