Publish Outlook calendars. What is server clock setting?

Question

I am working on a custom server implementation (VERY basic WebDAV) that accepts published Outlook calendars.

Outlook seems to have a parameter (see screenshot below) where it takes a parameter that forms a server that tells it how often to re-publish the calendar and what parameter I'm trying to figure out.

If the parameter is not specified, Outlook defaults to 60 minutes, which does not work for me, but I can not find any information about what the parameter may be (I know that Outlook parameters can be configured in the user interface, but I need to do this automatically through a response from the server). When using Wireshark, I see that the first time the calendar is published, Outlook sends the PROPFIND method to the PROPFIND URL:

 PROPFIND /path/to/url HTTP/1.1 X-Office-Version: 15.0.4771 Depth: 1 Content-Type: text/xml User-Agent: Microsoft Office/15.0 (Windows NT 6.3; Microsoft Outlook 15.0.4771; Pro) Host: example.com Content-Length: 114 Connection: Keep-Alive Cache-Control: no-cache <?xml version="1.0" encoding="utf-8" ?> <D:propfind xmlns:D="DAV:"><D:prop><D:resourcetype/></D:prop></D:propfind> 

which then responds with XML (I assume it will be a parameter, but cannot find any information on it):

 <?xml version="1.0"?><a:multistatus xmlns:a="DAV:"/> 

I got lost at this moment and don’t know where else I could follow a lot of search queries and traffic (Outlook Outlook Exchange messaging, but nothing I found seems to use the default setting). Any suggestion where it would be nice to look for something like that?

Answer 1

CalDAV (WebDAV Calendar Extensions documented in RFC-4791 ) uses iCalendar (an Internet calendar and scheduling of specifications for core objects documented in RFC-5545 so as not to be confused with Apple iCal) for data exchange. iCalendar supports non-standard properties starting with the prefix "X-".

X-PUBLISHED-TTL is a property that corresponds to the recommended update interval for subscribing to a calendar. It is supported by Microsoft for Outlook and Sharepoint, and possibly by some other calendar publishers, but not Google or Apple.

Example values:

 X-PUBLISHED-TTL:PT1H (every hour) X-PUBLISHED-TTL:PT120M (every 120 minutes) 

There is also some work in progress to officially add a similar property to the iCalendar specification. According to the latest version of the New Properties for iCalendar project, the new REFRESH-INTERVAL property will be used as follows:

 REFRESH-INTERVAL;VALUE=DURATION:P1W