In all previous versions of Office Outlook, delivery receipts worked all the time when checked. Since upgrading to Outlook 2013, I'm not receiving any delivery receipts. I’m aware that some mail servers do not respond, but I’m emailing recipients where their mail servers have always responded.
In particular, I sent an email (with delivery and read receipts requested) to a specific recipient on Wednesday (10 June 2015) morning. Within 10 minutes I received both delivery and read receipts. A short time later, my Office version was upgraded to 2013 and, once completed (a couple of hours later), I replied to the same recipient and again requested delivery and read receipts. I only received a read receipt and, to date, I’m still not receiving any delivery receipts from this and other recipients. However, I am receiving read receipts as normal.
For your info, I’m using a POP email account.
If it worked in the previous version, there is very clearly an issue that is associated with Office or Outlook that needs to be resolved.