I have issue with one external email sender. All e-mails he sends are rejected

>Subject: failure notice
>
>Hi. This is the qmail-send program at online.xxx.
>I'm afraid I wasn't able to deliver your message to the following
>addresses.
>This is a permanent error; I've given up. Sorry it didn't work out.
>
>:
>207.44.168.26 does not like recipient.
>Remote host said: 451 Could not complete sender verify callout Giving
>up.
>I'm not going to try again; this message has been in the queue too
>long.
>
>--- Below this line is a copy of the message.
>
>Return-Path:
>Received: (qmail 27999 invoked by uid 79); 29 Jun 2006 09:44:47 +0300
>Received: from 194.106.119.11 by wizard (envelope-from
>, uid 78) with qmail-scanner-1.25st
> (clamdscan: 0.88/1289. spamassassin: 3.0.2. perlscan: 1.25st.
> Clear:RC:0(194.106.119.11):SA:0(0.0/5.0):.
> Processed in 0.116937 secs); 29 Jun 2006 06:44:47 -0000
>X-Spam-Status: No, hits=0.0 required=5.0
>Received: from marjaex.standard.xxx (194.106.119.11)
> by wizard.online.ee with SMTP; 29 Jun 2006 09:44:47 +0300
>Received: from marjaex.standard.xxx [194.106.119.11]
> by marjaex.standard.xxx
> with XWall v3.36 ;
> Thu, 29 Jun 2006 09:44:46 +0300
>X-MimeOLE: Produced By Microsoft Exchange V6.0.6603.0
>content-class: urn:content-classes:message
>MIME-Version: 1.0
>Content-Type: text/plain;
> charset="us-ascii"
>Content-Transfer-Encoding: quoted-printable
>Subject: Vajaka
>Date: Thu, 29 Jun 2006 09:44:45 +0300
>Message-ID:
>
>X-MS-Has-Attach:
>X-MS-TNEF-Correlator:


When studied the issue i understood that my Exim mailserver is checking
by Message-ID: if sender's s account is valid.
But all sender emails are actually handled by/through online.xxx.
So there are no email accounts or even mailserver at marjaex.standard.xxx.
Is there any way I can allow that e-mails received from this domain are accepted ?

Turn off CALLOUTS. The option is under Exim Configuration Editor. Also, make sure your DNS is working properly. If its not, iy won't resolve properly.