Besides Domainkeys and DKIM, SPF record is also a popular method for email authentication. It is recommended to setup SPF record for your domain.
Setup of SPF record is simple, which only requires to deploy a TEXT record in your domain DNS server. Please refer to the following url for the details. http://www.microsoft.com/mscorp/safety/content/technologies/senderid/wizard/default.aspx
If you have any problem in DomainKeys/DKIM/SPF record implementation, please contact support@emailarchitect.net.