[Exim] valid RCPT command must precede DATA

OK so there's two Exim boxes on campus, A and B.

Box A accepts a spam from outside, and tries to forward it to B, which has
stronger defences and rejects at RCPT time on the grounds of callback.
B logs:


2003-10-09 16:59:38 H=A sender verify fail for <chang0220tai@???>

2003-10-09 16:59:38 H=A F=<chang0220tai@???> rejected RCPT
<someuser@???>: Sender verify failed

2003-10-09 16:59:38 SMTP protocol error in "DATA" H=A valid RCPT command
must precede DATA


Why the protocol error ? This implies the sender issued "DATA" even
though all the (one) recipients had been rejected.

Now if the sender were a piece of spamware I would understand. But here,
the sender is Exim box A, so should be following all the rules !!

For what its worth, here's the entry from A's log


2003-10-09 16:59:38 1A7dCQ-0002O4-BI <= chang0220tai@???
H=(ms1.securitinet.com) [65.110.12.181] P=esmtp S=2394
id=37903.762303113428100.78112@localhost

2003-10-09 16:59:38 1A7dCQ-0002O4-BI ** someuser@???
R=dnslookup T=remote_smtp: SMTP error from
remote mailer after RCPT TO:<someuser@???>: host B:
550 Sender verify fail


So why is it apparently proceeding to issue "DATA" ? Is this some sort of
pipelining issue I don't understand ?

FWIW, B is running 4.22, and I've seen this with various machines playing
the role of A, with different versions of exim, including 3.xx and 4.20

--
Chris Edwards, Glasgow University Computing Service