[Exim] Message: "result of an earlier callout reused"

I'm doing sender callout verification and every so often I get
warnings from an ezmlm list saying that mail to me is bouncing.

For example:

    63.205.225.170 does not like recipient.
    Remote host said: 550-Callback setup failed while verifying
    <modperl-cvs-return-4584-moseley=hank.org@???>
    550-(result of an earlier callout reused).
    550-The initial connection, or a HELO or MAIL FROM:<> command was
    550-rejected. Refusing MAIL FROM:<> does not help fight spam, disregards
    550-RFC requirements, and stops you from receiving standard bounce
    550-messages. This host does not accept mail from domains whose servers
    550-refuse bounces.
    550-Failed callout to address to <modperl-cvs-return-4584-moseley=hank.org@???>.
    550-Sender verify failed
    550 Contact postmaster+at+hank+org for help.

Yet, when I manually try the callout the sending MTA accepts the mail
from "<>" addressed to the address above without any problem.

I'm running Exim 4.34. Is there a way to get more details on this
failure? Can Exim log the SMTP sessions for verify failures?

Is there more info stored in the cache? Like when was the original
failure?



--
Bill Moseley
moseley@???