Nylas Connectivity APIs provide a solution to ensure that emails avoid spam filters with a 99.6% success rate by sending messages from the sender's individual email account, offering API-level control. For Ruby developers, the Nylas Ruby SDK simplifies the process of sending emails and attachments through the Nylas API. The guide walks users through checking and installing Ruby, particularly for Mac users, and setting up the Nylas Ruby SDK by managing dependencies like OpenSSL. It also details storing credentials securely using the dotenv gem and demonstrates sending emails and attachments with Ruby scripts. The process includes setting up the Nylas API client with user credentials and executing email dispatch through simple scripts, emphasizing ease of use and reliability for developers.