Deletemessagehash, generatemessagehash, keepmessagehash Channel Options

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Message hashes (deletemessagehash, generatemessagehash, keepmessagehash)

The generatemessagehash, keepmessagehash, and deletemessagehash destination channel options control whether the MTA generates, retains, or deletes a message hash. respectively. deletemessagehash is the default. All of these channel options first apppeared in the 6.3 release. These keywords are intended to be used in conjunction with message archiving

Note that AXS:One archiving will generate its own message hash on the messages it receives, if the MTA has not already generated and inserted such a message hash. However, in order to correlate messages in the Message Store with the messages archived by AXS:One, it is necessary that the MTA generates the hash and that that hash is retained in the messages delivered to the Message Store. Therefore, channels that deliver to the Message Store (ims-ms or tcp_lmtpcs* sorts of channels) should be marked either generatehash or (if the message hashes are being initially generated at an earlier channel stage) keephash. In contrast, a channel delivering to remote Internet hosts, such as typically the tcp_local channel, would typically be marked deletehash even if messages going out tcp_local are being archived, since there would in general be no expectation that the remote Internet sites would do anything (get any benefit) from the message hashes.

The choice of which channel(s) to mark with generatehash will depend upon how "soon" vs. "late" one wishes to choose to consider a message's essential characteristics to be established. Generating a hash "early" (as soon as a message first comes into the MTA) may be before various changes (e.g., changes performed by the conversion channel) occur, or before "split up" of a message into separate copies for different classes of recipients. More "different" (in one way or another) "copies" of a message may be considered "the same" for the archival purposes when hash generation is performed "early". Whereas when hashing is performed "late" (at the final delivery channel stage), then additional sorts of differences in message "copies" can be reflected in the message hash value (more distinctions between "copies" occur). But this may be either a plus or a minus depending upon site goals.