We will soon replace the email library of Copernica Marketing Software. This library is responsible for both generating MIME messages (it turns an email object into a string) and for doing the opposite: to parse MIME strings into useful objects.
DKIM: DomainKey Identified Mail
DKIM stands for DomainKey Identified Mail and is also a piece of code within the DNS. It places a unique digital signature in the header of your email that labels you as a safe sender. Receiving mail servers will see if the email was truely sent by you and was not forged or forwarded by someone else. However, most providers will not mind when a DKIM is not properly set. DKIM is not yet widely supported. Yahoo and Gmail, among others, perform a strict check on DKIM to filter out spam messages.
A domain protected by DKIM is not interesting to spammers. The chances of their messages reaching a recipient's inbox are a lot smaller. As a benefit, domains protected by DKIM are less abused by spammers. Copernica therefore recommends setting DKIM as a form of email authentication and as a tool for optimizing your deliverability.
How does DKIM work?
An email message consist of ones and zeros. This means you can sum up these numbers to a total. This total is encrypted and included as a code in the email. The mail server that receives your email deciphers this code with a key that is extracted from your DNS data. The mail server will sum up the data in your email as well at the same time it deciphers the code. If the sum in your DKIM matches the sum the mail server calculates, your email is considered authentic and allowed through to the inbox.
Please note: DKIM does not block emails that are not authentic. It will mark these messages as being invalid. Based on this mark, a spam filter can either block an email or label it 'suspicious' or as spam.