FSC-0031                                            May 1, 1989

          EchoMail ^aEID: Dup-Checking with Linked Replies
      A Proposal To The FidoNet Technical Standards Committee

Currently, no universal methodology for implementing echomail
duplicate message checking exists.  One thing is certain - they
will only increase in number as the shear volume of echomail is
increasing every day!

In order to catch the highest percentage of duplicates possible
it is desirable to utilize a system which actually tags each of
the messages themselves with a distinct messages identifier to
be used to check against an existing database of all previous
messages' identifiers.  In practice, this is not possible, but
we can limit the number of previous identifiers kept so that
processing is quick but still almost certain to eliminate any
duplicate messages.

This also provides an easy method of linking replies to their
original message by appending the previous identifier.  Using
a linked reply technique allows easy relinking of the messages
to the original message, assuming it still exists.

This proposed ^aEID: kludge line specifications are as follows:

1)  A 16-bit CRC followed by a 32-bit DOS file date/time stamp.

2)  The 16-bit CRC is calculated by first CRC'ing all but the
    first 11 (static) characters of the origin line, followed
    by the first two "words" of the from name, the first two
    words of the to name, and the first 25 characters of the
    subject line after stripping leading occurances of "Re: "

Notes:  You must always upper-case the to/from/subject fields,
  as some current processors will change the case of that text.
  Using only the first two words of the from and to names will
  eliminate the potential problem when some processors add the
  " of xxx/yyy" to the end.  Stripping all leading occurances
  of the "Re: " in the subject field is also done to eliminate
  the possibility of changed subject lines not matching with
  the original message, which is also the reason for limiting
  the length of that field to the first 25 bytes (after taking
  off all the "Re: " sequences), because adding the leading
  "Re: " may force characters out (because they are beyond the
  72-character field limit).

When you must add an EID line for a message which is not local,
you have to zero the seconds field before creating the 32-bit
time stamp - some processors eliminate this information!  This
limitation can be overcome if most editors insert them at the
time they are written.

Automatic reply linking
========= ===== =======

When replying to a message with an ^aEID: line, extend the new
^aEID: with the ^aEID: fields of the original message.  The new
line would look like this:

^aEID: xxxx yyyyzzzz uuuu vvvvwwww

Where 'uuuu vvvvwwww' is the Eid information of the original
message.  Only one previous message's information is retained.