De-duping attachments

[Shuvam Misra]

> Makes sense.  There might be some size based logic here too - only
> bother applying this on messages over 20k, and where the attachment
> is at least 20k in size.  Anything smaller than that is pretty
> pointless.

Yes, absolutely. Left to myself, I'd not have bothered with any
attachment less than 100KBytes or so. The stuff that gets my goat is
seeing our customers using email to shunt 20MB CAD files back and forth
across the world two dozen times. Emails are being used for the kind of
work God had meant trucks to do. :(

> Sure.  Ideas are good :)  I don't think I'm sold on the value though.
> And given that Rob is actually the one who argued me down from
> implementing this years ago ;)  But maybe our use case isn't the
> same as yours.

Let me get some hard data from a few of our large corporate clients'
servers, and then we'll talk again. May take a couple of weeks to get
this data, because we'll need to look for a time window when the mail
server is less loaded to run our scan.

Shuvam