John Levine wrote:
For a while I used a very aggressive greylister which soft failed
after the dot, kept a hash of the message, and wanted to see an
exact copy with the same hash to let the message through. I stopped
using it, but not because of SMTP problems. (A surprising number of
ESPs reconstruct the message rather than retransmitting it, so the
hash didn't match.)
Yes. And unlike bots, ESPs will do retries. (Lord knows they do retries,
even on 550 errors.) At Habeas I had a customer that set the Date field
at connect time and generated no Message-ID field at all; and they
complained to /us/ when we logged duplicates!
I haven't seen that problem as much as I used to, though. As the volume
demands on the have grown, the software developers seem more inclined to
do more computation in advance and less at delivery time.
<csg>