SSL has no direct role in deliverability. That is primarily DKIM's role.
SSL (Secure Sockets Layer) is a standard security technology for establishing an encrypted link between a server and a client - typically a web server (website such as GMail or Yahoo! Mail) and a browser; or a mail server and a mail client (e.g. Apple Mail, Mozilla Thunderbird, Microsoft Outlook).
DomainKeys Identified Mail (DKIM) lets an organization take responsibility for a message that is in transit. The organization is a handler of the message, either as its originator or as an intermediary. Their reputation is the basis for evaluating whether to trust the message for further handling, such as delivery. Technically DKIM provides a method for validating a domain name identity that is associated with a message through cryptographic authentication.
DKIM attaches a new domain name identifier to a message and uses cryptographic techniques to validate authorization for its presence. The identifier is independent of any other identifier in the message, such in the author's From: field.
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