[exim] sender verification callout

Quick question...... May be nothing, but oh well.

2005-05-30 16:11:41 SMTP connection from [159.148.xxx.xxx] I=[aaa.aaa.191.122]:25 (TCP/IP connection count = 1)
2005-05-30 16:12:46 H=frog.abc.com [159.148.xxx.xxx] I=[196.30.191.122]:25 sender verify defer for <mk@???>: Could not complete sender verify callout
2005-05-30 16:12:46 H=frog.abc.com [159.148.xxx.xxx] I=[196.30.191.122]:25 F=<mk@???> temporarily rejected RCPT <c.knipe@???>: Could not complete sender verify callout
2005-05-30 16:12:47 H=frog.abc.com [159.148.xxx.xxx] I=[196.30.191.122]:25 incomplete transaction (QUIT) from <mk@???>
2005-05-30 16:12:47 SMTP connection from frog.mt.lv [159.148.xxx.xxx] I=[aaa.aaa.191.122]:25 closed by QUIT


however:

Trying 159.148.xxx.xxx...
Connected to mailgw.abc.com.
Escape character is '^]'.
220 mailgw.abc.com ESMTP abc.com Mon, 30 May 2005 17:19:59 +0300
ehlo pyro.xyz.com
250-mailgw.abc.com Hello pyro.xyz.com [aaa.aaa.191.122]
250-SIZE 52428800
250-PIPELINING
250 HELP
mail from: exim@???
250 OK
rcpt to: mk@???
250 Accepted
quit
221 mailgw.abc.com closing connection
Connection closed by foreign host.

Why is the verification failing??? Timeout perhaps? anyway to debug this without
putting the entire server into debug mode?? It's only doing this with 1 or 2
domains...


--
Chris.