DomainKeys is an Internet standard to authenticate that emails really come from their claimed domain. It also ensures that a message’s contents remain unaltered during transit.
If you see:
DK Email not accepted for failing DomainKey authentication. Please visit http://help.yahoo.com/l/us/yahoo/mail/yahoomail/technical/technical-16.html
…then your email wasn’t accepted because it failed authentication against your sending domain’s DomainKey policy.
We only reject emails for failing DomainKey authentication when both of these conditions apply:
a) the domain name of your email address (whatever’s after the @ symbol – ‘example.com’ for ’email@example.com’) has a published DomainKey policy explicitly indicating that all emails from the domain must be signed and authenticated with DomainKeys to prevent forgery; and
b) the rejected email couldn’t be authenticated against your domain’s policy due to a missing or bad DomainKey signature.
If you were the original sender and you believe you received this error for a message that should be accepted, please let us know by submitting the full text of the error message you received. We also strongly recommend that you contact your domain’s mail administrator and make them aware of the problem.
For more information on DomainKeys, please visit this page.