DKIM (DomainKeys Identified Mail) and SenderID are two email authentication technologies that have been shown to improve email delivery rates, with the customer in question seeing a significant increase in inbox delivery after implementing these measures.` `The customer's issue was resolved by identifying the problem as being related to the lack of DKIM and SenderID setup on their domain, which allowed the email to be blocked by Postini's spam filter, and then successfully sending an identical email from a different domain that did have these settings in place.` `This case study highlights the importance of setting up DKIM and SenderID for email authentication, as it was found to make a significant difference in delivering emails to the inbox, with one expert even stating "DKIM and SPF on your own domain are critical for email delivery. Skip it at your own risk."