Home > Support > Knowledge Base > Article

FAQ: Explanation of the Automatic Recipient Detection Feature

The automatic recipient detection feature in Exchange Connector allows messages to be routed to Exchange mailboxes without manually associating an Exchange mailbox with every POP3 account. This is designed for the scenario where a single POP3 mailbox receives messages for multiple users in Exchange, for example, a global catch all mailbox that handles all messages for the domain.

The operation of email systems and the SMTP and POP3 protocols mean that careful planning is required to avoid complications in this configuration. As a result, the automatic recipient detection delivery configuration is not recommended for scenarios other than a global catch-all mailbox, due to the increased complexity involved. It should only be used where manual recipient selection is not possible.

Understanding the Automatic Recipient Detection Feature

The automatic recipient detection feature relies on the message header containing the email address of the recipient. This is not always the case in email systems and is not a requirement of most mail servers. In fact, the message header may not contain any email addresses which are associated with any Exchange accounts. This is likely, although not limited to, messages where the recipient was a Bcc recipient, or the message was sent to an externally-managed mailing list.

Exchange Connector has several features to ensure reliable delivery even in complex scenarios. However, there is no single configuration that works with all POP3 servers or is the "correct" configuration. All POP3 servers are slightly different and it is likely that some testing and experimentation may be necessary to determine the optimal configuration.

Quantum Software Solutions strongly advises that users manually test the scenarios of Bcc recipients and several different mailing lists prior to deploying the automatic recipient detection feature with a POP3 server if its exact behaviour in these scenarios has not been previously verified. Test messages need to be sent from accounts which are completely separate from the Exchange environment. Web-based free email services are ideal for keeping an account solely for the purpose of testing and troubleshooting mail delivery scenarios.

It is possible that some POP3 servers may not be able to be used correctly with the automatic recipient detection feature, even if they claim to support global "catch all" mailboxes. Our Technical Support services will be happy to perform some tests and analyze your configuration if you are unable to get automatic recipient detection to work, or suspect this to be the case. If we determine that the POP3 server is not compatible with this feature, we will advise on alternative deployment options and but will not be able to support the feature in your environment.

Scenarios affecting Automatic Recipient Detection

To and Cc Headers

In the case of many messages, the recipients' addresses will be contained within the To or Cc header of the message and it will be delivered correctly with no further configuration.

In the case of the To and Cc headers being absent or blank, Exchange Connector will need an alternate means of locating a recipient. Otherwise, it will be unable to deliver the message and a failure report will be generated.

Bcc Headers

In order for the Bcc feature to truly conceal addresses from other users, even the mail systems involved in transmitting the message are not aware of any of the contents of the Bcc header. This means that a message downloaded from the POP3 server which was sent to a Bcc recipient will not contain the recipient's address in the To or Cc headers. The Bcc header does not even exist in messages sent by most mail systems, even if they contain Bcc recipients.

Some mail servers which support "catch all" mailbox functionality have the option to add a Bcc header to messages. This is done by the receiving mail server fabricating a Bcc header. The fabricated header contains only the recipient's address to the Bcc header. This is always known to the receiving server at the exact time of delivery (via the SMTP RCPT TO command). In the absence of a POP3 connector, the RCPT TO command would be the usual way of the mail server determining the final destination of the message - headers are never used for this purpose without a POP3 connector.

If the POP3 server supports this feature of adding Bcc headers, it must be enabled for Exchange Connector to be able to be supported by Quantum Software Solutions.

Additional Special Headers

Some mail systems are provide the same functionality as fabricated Bcc headers by injecting the recipient's address into another special header on the message. These special headers can be manually specified in Exchange Connector by using the "Define Custom Headers" button in the recipient configuration.

For example, Gmail creates a Delivered-To header for all messages delivered. Other headers commonly used for this purpose include Original-recipient, X-Original-To and Envelope-To. The headers used depend largely on the mail server and their implementations are not standardized.

Received Headers

Many mail servers add the recipients' addresses to the Received header, which is present on virtually all Internet-delivered email messages. The format of this field is however very non-standard across different mail servers and a particular mail server cannot be assumed to use this header in a way which is compatible with Exchange Connector, without doing some testing.

The option "Also search the received header" will attempt to extract addresses from this header. Unless a special header (as described above) is added by the POP3 server, it is recommended that this option be enabled.

However, relying on this option for locating recipients' addresses should be considered a last resort. Due to the unpredictable format of the "Received" header, it is likely that some messages will occasionally not be able to be delivered via this header, causing delivery failure reports to be generated by Exchange Connector.

POP3 mail servers which are not able to add either Bcc headers, or other special headers to the message, do not support "catch all" mailboxes properly and completely reliable delivery to the intended recipients cannot be guaranteed. Quantum Software Solutions will not support automatic recipient detection in the Bcc or mailing list scenarios with such servers, unless the Received header detection method can be tested to be adequate with that specific server.

Selection of a Last Resort Recipient

You can select the option "If the recipient cannot be detected, deliver messages to this recipient", to have Exchange Connector fall back to manually delivering messages if necessary. It is recommended that you enable this option.

Other Articles