SMTP Smart Host and Outgoing Mail Relay Support for Eenos

Feature Overview

Introduce global SMTP Smart Host support in Eenos, allowing server administrators to route all outgoing email through an external SMTP relay service instead of delivering messages directly from the hosting server.

This feature will help hosting providers improve email deliverability, use trusted outbound email filtering services, and overcome network restrictions such as blocked outbound SMTP port 25.

The Smart Host configuration will be managed centrally through the Eenos root administration panel and integrated with the existing Exim mail server.

Proposed Features

1. Global Smart Host Configuration

Provide a centralized interface for configuring a server-wide SMTP Smart Host.

• Enable or disable global Smart Host routing.

• Configure the SMTP relay hostname or IP address.

• Support configurable SMTP ports, including 25, 465, and 587.

• Support authenticated and unauthenticated SMTP relays.

• Configure SMTP authentication username and password.

• Support STARTTLS and implicit TLS encryption.

• Save and apply configuration changes through the Eenos interface.

• Restore direct email delivery when Smart Host routing is disabled.

The configured Smart Host will apply to all outgoing email from hosted domains and accounts on the server.

2. SMTP Authentication and Security

• Support standard SMTP AUTH mechanisms, including PLAIN and LOGIN.

• Securely store SMTP authentication credentials.

• Protect sensitive credentials from unauthorized access.

• Validate TLS certificates for encrypted SMTP connections.

• Allow administrators to update credentials without exposing existing passwords.

• Provide a connection test to verify SMTP relay availability and authentication.

3. Exim Mail Server Integration

Integrate Smart Host configuration with the existing Eenos Exim management system.

• Automatically generate the required Exim router, transport, and authentication configuration.

• Apply configuration changes through the existing Exim configuration rebuild process.

• Route outgoing internet email through the configured Smart Host.

• Preserve local email delivery between hosted accounts.

• Ensure queued messages remain available for retry when the relay is temporarily unavailable.

• Restore standard Exim delivery behavior when Smart Host support is disabled.

4. Third-Party SMTP Relay Compatibility

Support standard SMTP relay services, including:

• SpamExperts / N-able Outgoing Filtering

• Amazon SES SMTP

• Mailgun SMTP Relay

• SendGrid SMTP Relay

• SMTP2GO

• Other SMTP-compatible relay providers

The implementation should use standard SMTP protocols without requiring provider-specific integrations.

5. Mail Queue and Delivery Monitoring

Integrate Smart Host routing with the existing Eenos Mail Queue Manager.

• Monitor outgoing messages routed through the Smart Host.

• Display SMTP relay errors and delivery failures.

• Support retrying deferred messages.

• Record authentication failures, connection errors, and relay rejections.

• Preserve existing Exim delivery logs and queue management operations.

6. Reliability and Security

• Prevent exposure of SMTP credentials in application logs.

• Restrict Smart Host configuration to root administrators.

• Preserve compatibility with SPF, DKIM, and DMARC.

• Avoid unintentional direct delivery when the Smart Host is unavailable.

• Maintain normal incoming email and local mailbox delivery.

• Ensure all externally routed messages follow the global Smart Host configuration.

Technical Considerations

The implementation should use the existing Eenos Exim configuration generation system and root administration interface (WAP).

Smart Host settings will be stored centrally and applied during Exim configuration rebuilding.

Only one global Smart Host configuration will be supported per server. Per-domain, per-user, and per-account relay configurations are outside the scope of this feature.

Existing email services, including forwarders, autoresponders, email filters, SpamAssassin, ClamAV, DKIM, and Mail Queue Manager, must continue functioning normally.

Expected Benefits

• Improve outgoing email deliverability.

• Enable integration with trusted outbound SMTP relay providers.

• Support hosting servers with restricted outbound SMTP connectivity.

• Simplify outgoing email routing configuration.

• Reduce manual Exim configuration requirements.

• Provide centralized management of external SMTP delivery.

• Improve outgoing email reliability and troubleshooting.