Too many "false positives" !?!

Hi,

I'm testing greylisting with postgrey and postfix on my mailserver.

Within two days I got so many "false positives", 1st rejected by
greylisting and then the remote MTA does not retry to deliver the mail
for hours, for days ... even major providers like web.de do only try
once and then generate a delivery error.

That does not correspond with the promises on several wesbites claiming
almost no false positives from greylisting. Didn't they counter-check?
Are there so many non-RFC-compliant MTAs out there? Or what's going
wrong here?

It's an underdog job to check for false positives, not to mention
repairing the communication damage.
And I can't whitelist all innocent non-RFC-comnpliant MTAs on the world.

Additionally some web-mail providers like hotmail hide the greylisting
error message from their customers, generating a delivery failure
message of their own, if they notify at all.

disappointed regards

orinoco