[dkim-ops] Newbie: How do I test a dkim setup

[ram]

I am supposed to implement DKIM for our outgoing mails

I am planning to use dk-milter in postfix. Since we use postfix on our
mailservers

Before implementing DKIM ( I have little idea of ) , I would just like
to to test out various things. 

I would like to know if there is some commandline dkim sign utility

Can I just create a mailfile using "vi" and dkim-sign & sendmail it
using some script. So that I can see what the dkim signed file looks
like and test everything before implementing dkim on all servers.