Missingrecipientpolicy Channel Option

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Legalizing messages that lack any recipient headers (missingrecipientpolicy)

RFC 822 (Internet) messages are required to contain a recipient header line: a To:, Cc:, or Bcc: header line. A message without any such header line is illegal according to RFC 822. Nevertheless, some broken user agents and mailers (e.g., many older versions of sendmail) will emit such illegal (per RFC 822) messages.

Note that RFC 2822, the update to RFC 822, relaxes the RFC 822 requirement and allows submitted messages to be lacking in any recipient header line. However, unless it is certain that all the MTAs and MUAs that may ever handle a message in fact conform to RFC 2822 (rather than the older RFC 822), it is unwise to emit a message lacking all recipient header lines, since the behavior of an RFC 822-compliant MTA or mail user agent may be undesirable when encountering a message that is, from its point of view, illegal---results may include rejection of such a message, potentially undesired exposure of recipient information such as recipients intended as Bcc: recipients, etc.

The missingrecipientpolicy channel option takes an integer value specifying what approach to use for such messages; the default value, if the channel option is not explicitly present, is to use the MTA option missing_recipient_policy value (which itself defaults to 0, if not set, which as of JES MS 6.2 is equivalent to a value of 1 meaning that messages are passed through unchanged---in JES MS 6.0 and JES MS 6.1 the default value of 0 had been equivalent to a value of 2 meaning that envelope To: addresses are placed in a To: header).

Value	Action
0	Use current best practices to resolve the situation. Prior to 6.2 this was the same as 2, in 6.2 and later it is the same as 1.
1	Pass the illegal-per-RFC 822 (though legal per RFC 2822) message through unchanged.
2	Place envelope To: recipients in a To: header.
3	Place all envelope To: recipients in a single Bcc: header.
4	Generate an empty group construct ( i.e., ;) To: header line. The phrase used in the group construct is controlled by the missing_recipient_group_text MTA option, so for instance " To: Recipients not specified: ;".
5	Generate a blank Bcc: header.
6	Reject the message (with a "554 5.6.0 message is missing required recipient header fields" error).

Note that the missing_recipient_policy MTA option can be used to set an MTA system default for this sort of behavior.