"DKIM" stands for DomainKeys Identified Mail. DKIM creates a domain-level authentication framework for email by using public-key technology and DNS record to prove the source and content of a message.
You can find general information about DKIM at http://dkim.org/ and the DKIM FAQs at http://dkim.org/info/dkim-faq.html.

Field |
Description |
Active |
Check this box to enable DomainKeys technology for sending messages from this Domain. The Enable DKIM feature in Global Settings Domains must be checked for this option to be available. |
Selector |
Specifies the domainkey used to sign an outgoing email. There can be only one valid selector at a time. |
Domain |
Specifies the Domain or subdomain for the DomainKeys technology to use. Leave this blank and the actual Domain will be used. |
Private Key |
The Private Key that is used by DomainKeys. You can use the Generate Private Key button to create a file containing your Private Key. |
Selector Data |
Contains the Selector Data which contains your Public Key. Use the Retrieve selector data button to populate this field. This field contains the string that should be included in your DNS TXT record. The format of the DNS TXT record is: <Selector>._domainkey.<domainname> <Selector data> |
Generate private key |
Use the button to compute your Private Key. |
Retrieve selector data |
Use to Generate the Selector Data based on the private key and key length. The selector data contains your Public Key. |