Can any one gave me requirements/step-by-step procedures on how am I suppose to create DomainKeys for my mail server so that our email can pass through on Yahoo!'s mail server without being marked as spam or bulk mail?
I think implementing DomainKeys is one of the requirements of Yahoo! Mail to not have email marked as spam.
Our mail server is hmailserver.
DKIM is a "standard".
Wikipedia will give you the links to the specification of how it works, however it does require changes both to dns and to mta. I don't know hmailserver, so the actual step-by-step is up to somebody else to fill in.
In short a dkim implementation hashes the mail using a key that is published using dns. The receiving end finds your key via dns lookup and compares that to the hash included in the mail. If they match the mail is from the domain that it claims it's from.
dkim.org is the place to go for information on DomainKeys Identified Mail. You might also find the Wikipedia article on DKIM worth reading.
Basically, you need to create at least one public/private key pair, publish the public key as a DNS record, and change your mail software to sign outgoing messages using the private key.
Here's a list of software that implements DKIM.
Check out this youtube video, it explains domain keys: http://www.youtube.com/watch?v=7_K7Pi_y9Jg
Also note that just implementing domain keys will not guarantee your email gets through the Yahoo spam filter. Even with everything setup 100% to their guidelines, you will probably still need to submit a request to white-list your mailer to guarantee delivery.