[exim] DKIM key configuration for multiple domains

Hi,

Is there any way I can setup DKIM for multple domains?

I setup DKIM for one domain and DKIM result is pass. And when I use same
DKIM public key for my another domain, DKIM signature is attached but
message header shows DKIM=fail.

Here is the test results on message header.

*Mydomain1.com - DKIM result*

Authentication-Results: mx.google.com;
       spf=pass (google.com: domain of root@??? designates
SERVER-IP- as permitted sender) smtp.mail=root@???;
       dkim=pass header.i=@
mydomain1.com

****************

*Mydomain2.com - DKIM results*

Authentication-Results: mx.google.com;
       spf=hardfail (google.com: domain of test@??? does not
designate SERVER-IP as permitted sender) smtp.mail=test@???;
       dkim=fail header.i=@mydomain2.com
DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed;
d=infiserver.com; s=fusion5;
    h=Date:From:Message-Id; bh=f7kChJIPrUaTEZXIizmQd6A20Xu2MUdYf3GaZ5bir08=;
    b=fhOfwkD3aVnd5V+ZRvF+V0sDRC20ihbjBd+UzFGOIwey+sgQzD5Uupk7li3ejNX+QEXdCdRqCsmrDca79dAoqRJi9F895Sz2ClHgQpRFnItqgGvd0Vu/evBKkFRfukVXWUMCkMcPXVa5/hpenaswyt1zA7KoTs+XwiCZ2AS/JNE=;

How do I resolve this., can anyone let me know where and what steps need to
take for resolving this issue?

-
Smarthost