Restricting SMTP inbound routing

You can set up your Domino® system to control, verify, and restrict inbound mail. Restricting inbound mail routing prevents Domino® from accepting unwanted commercial e-mail (UCE) sent to your users and consequently reduces the load on your system.

In addition, on servers that receive some of their inbound mail over Notes® routing, you can restrict routing based on Domino® domains, organizations, and organizational units.

Table 1. SMTP Inbound Controls tab
Tab See this topic
Inbound Relay Controls Setting inbound relay controls
Inbound Relay Enforcement Specifying enforcement of inbound relay controls
DNS Blacklist Filters Enabling DNS blacklist filters for SMTP connections
DNS Whitelist Filters Working with DNS whitelists for SMTP connections
Private Blacklist Filter Working with private blacklists for SMTP connections
Private Whitelist Filter Working with private whitelists for SMTP connections
Inbound Connection Controls Restricting inbound SMTP connections
Inbound Sender Controls Restricting who can send Internet mail to your users
Inbound Intended Recipients Controls Restricting users from receiving Internet mail

Error handling of messages rejected by SMTP inbound controls

The inbound SMTP restrictions are enforced by the SMTP Listener before a message is accepted, rather than by the Router after a message is already in the system. This difference in where restrictions are enforced affects how errors are handled when a message is rejected. When a Router restriction results in a message being rejected, Domino® returns a failure message stating the reason for the failure to the sender. Domino-generated nondelivery reports contain default text, which you can customize. For example, when you configure a maximum message size for a server, Domino® checks the size of the message only after it is received in MAIL.BOX. If the message exceeds the configured size, the Router generates a failure message to the sender.

However, if you set an SMTP restriction that causes Domino® to reject an inbound message, the SMTP listener returns a permanent error during the SMTP transfer; the message never enters the server. In this case, it is the responsibility of the originating SMTP server to generate a failure message to the sender. For example, if both the receiving Domino® SMTP server and the sending SMTP server support the ESMTP SIZE extension, and the Domino® server is configured to honor a maximum message size, when the Domino® SMTP listener receives a message that exceeds the defined limit, it rejects the message before it is ever received and returns a permanent error to the sending server. You cannot use Domino® administrative tools to customize the server's SMTP response.

Using Extension Manager to customize the server's SMTP response

You can control the content of SMTP responses using SMTP logical function hooks available in the Extension Manager services of the C API Toolkit for Notes/Domino.