req Unique Msg Id

1.3.6.1.4.1.334.3.1.2.2.1.6

Specifies a unique message id used internally by the MTA for identification of a message. This form of the message id may or may not be identical to the inbound and/or outbound forms of the message id. If specified, this may be the only search criteria required. Set to an empty (zero length) string if unknown or irrelevant to query.