One of the most important metric in any email campaign is the number of recipients who have opened the email. The open rate is the ratio of the number of recipients who opened or read the mail to the number of recipients the email campaign was sent to. The recipient open or read is tracked by embedding a single pixel image in the message, which when opened (by image enabled email clients either manual or automatic) is recorded in the email server as an open. There are other indirect techniques as well. How to make your recipients open the message, when they see the mail in their inbox?