SpamfilterN received MTA options

Spamfilter MTA options:    (0-7)
Some spam/virus filter packages operate best if provided with the "current" Received: header line -- the sort that the MTA will be generating for actual prefixing of the message, but subsequent to the spam/virus filter package scanning. A     MTA option controls whether the MTA generates a most recent Received: header line to pass to the Nth spam/virus filter package. This is a bit-encoded value, but any nonzero value specifies that the MTA does pass a pseudo-Received: header line to the spam/virus filter package. Note that this pseudo-Received: header line is not necessarily exactly what the MTA will truly end up inserting, but it does contain the same routing information (in particular client source IP address) which tends to be the item of especial interest to spam/virus filter packages. SpamAssassin in particular tends to operate better when provided with such a Received: header line. Bit 1 (value 0) in the option is used to cause the header to be generated without any additional options. New in Messaging Server 7.0.5 is support for the bit 1 (value 2), which means to pass  the spam/virus filter package a synthesized Received: header line that includes an additional clause: (envelope-sender mail-from-address) Some SpamAssassin configurations use such a clause in the Received: header line as the source of MAIL FROM addresses instead of using the standards-compliant Return-path: field.

As of the 8.0.1 release, bit 2 (value 4) is used to specify that the header not be generated during reprocessing operations. (This is useful since the enqueue to the reprocess channel already added a Received: header field.)

See also:
 * Process and reprocess channels
 * Spamfilter MTA options