Milter-greylist

Oliver Fromme wrote:
> 
> I'm already aware of all of that.
> 
> But isn't it possible that -- in theory -- the client side
> closes the connection as soon as the headers are received
> during the data phase? 

Yes, in theory but milter-greylist isn't the one holding the connection. 
Sendmail is.

Milter-greylist is a milter under sendmail, and thus is also limited by the 
milter API, which dictates at what points Sendmail will check with it.

AFAIK, sendmail calls milters for error codes at the end of each command, but 
not in the middle of any of them.

> A compliant mail server has to
> treat that like a 4xx temporary error.

True, but I'd also expect that intentinally relying on this violates the RFCs, 
and would likely result in at least some server admins blacklisting you for it. 
I wont swear to it, but I'd be very shocked if this was considered RFC compliant 
behavior to engage in intentionally.

I'd also not be surprised to find that some popular MTA's don't handle this 
condition properly.

> So you would have
> to receive all the headers, but not the mail bodies.
> Actually I thought that milter-greylist already supported
> something like that.

Milter-greylist doesn't support anything like that, and can't because Sendmail 
doesn't support anything like that.

You'd have to write your own MTA to do that.