There's some exciting stuff in the Zimbra 6.0 Roadmap that Zimbra has posted. One glaring omission is read receipts and delivery reports which is by far the most requested missing feature.
Bug 7257 – Support read receipts and delivery reports in webmail
I was somewhat concerned about this because at the same time someone commented that the feature had been pushed to 6.5 and the RFE was marked as private.
Anand Palaniswamy from Zimbra quickly responded that this was in error and that this was still slated for 6.0. However, it's a little bit of a concern that such a widely requested feature failed to show up in the roadmap document.