Postmark, an email service provider, emphasizes the importance of authentication in sending emails. Over 61% of their customers authenticate their emails, which helps prevent delivery issues and spam filtering problems. Postmark has built-in setup processes for SPF records and Domain Keys, and most of its customers have their Sender Signatures set up correctly with DKIM and/or SPF. ISPs use tools like engagement and content scanning to verify the authenticity of emails, making it crucial to sign emails to remove doubt. The company recommends using email authentication as a best practice, stating that not doing so can lead to difficulties in getting emails delivered. Postmark provides resources and simple steps for customers to set up their Sender Signatures with DKIM.