A secure correlation identifier (SCID) for authentically correlating notifications received from event sources with subscriptions, a SCID authentication system and method of filtering unsolicited messages are provided. The SCID comprises a correlation identifier for making the SCID unique, a sequence of bits concatenated with the correlation identifier and a secure tag concatenated with the concatenation of the correlation identifier and the sequence of bits. The system comprises a SCID generator for generating a SCID to be used in a message and a SCID authenticator for authenticating the SCID. The method comprises the steps of receiving a notification message having a SCID, verifying that that SCID is authentic, accepting the message if the SCID is authentic and rejecting the message if the SCID is not authentic.