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Table of Contents

The "Filtering Points" Concept

This section explains the Filtering Points in ORF.

SMTP Transport Filtering

The SMTP network protocol is the transport protocol for emails. ORF integrates with the Exchange transport under Microsoft® Exchange 2007 and newer versions (or with the Microsoft® IIS SMTP Service under Exchange 2000/2003) to filter specific SMTP protocol events.

SMTP Sessions and Filtering Points

Simplified scheme of SMTP sessions and filtering points

The scheme above describes a simple SMTP session and the filtering points in the SMTP protocol event scheme.

  1. The sender server introduces itself and the SMTP transport responds with a description of its capabilities ( SMTP commands: EHLO or HELO)

  2. The sender server specifies the sender email address, e.g., [email protected] (SMTP command: MAIL FROM)

  3. The sender server specifies one or more recipient email address for the message to be sent (SMTP command: RCPT TO). ORF performs filtering on this protocol command event and may reject the recipient depending on the results of the filtering.
    This is the Before Arrival filtering point.

  4. If at least one of the recipients were accepted, the sender server issues a DATA or BDAT command and starts sending the email.

  5. ORF goes active again when the entire email has arrived and the sender server expects response from the local SMTP server. On this event, ORF filters again and performs the necessary action based on the filtering result.
    This is the On Arrival filtering point.

  6. The sender server closes the SMTP session by sending the QUIT command to the local SMTP server.

The Before Arrival Filtering Point

Find more about this filtering point in the Before Arrival Filtering Point section.

The On Arrival Filtering Point

Find more about this filtering point in the On Arrival Filtering Point section.

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