Hi, CalServer switched to use URNs/UIDs as ATTENDEE identifies. I think thats a really BIG mistake, I feel very strongly about it ;-) and would like to see that behaviour modified. Currently: ATTENDEE;X-CALENDARSERVER-EMAIL=abc@def.de:urn:uid:29838484... should be ATTENDEE;X-CALENDARSERVER-UID=29838484:mailto:abc@def.de or even ATTENDEE;X-CALENDARSERVER-UID=29838484:tel:+49-12234-233 Why? There are two big reasons: a) Interoperability. I would claim that all iCalendar clients use mailto ids today. Plus plenty of other iCalendar infrastructure. Changing this will result in interop issues and breaks a lot of stuff for (IMO) no good reason. b) The URN is completely opaque/proprietary to the client. It can't possibly resolve a URN to a contact database or other things which relate to attendees. This results in bad user experience and cross app integration at multiple levels. Note that my suggestion still includes a server specific UID which can be used for a stable resolution - as long as clients preserve it. And if not, its still sufficient for the far majority of real world deployments (reassigning email addresses is a no go, don't understand why people even consider that :-). Cyrus claims that this is not viable because clients throw away X- attributes. Does iCal do that? I think Kontact, Evo, Moz are all preserving such (we certainly do). Note: I'm fine with emitting URNs for stuff which can't possibly be resolved. Resources or locations _might_ be in that category, though I would still prefer an LDAP URL (+ UID X attr) if they are backed by something like OD. This still gives the client a way to learn about the ATTENDEE. Thanks a lot, Helge -- Helge Hess http://helgehess.eu/