title: What does TZOFFSETFROM and TZOFFSETTO mean
body: <p>I am trying to send an outlook appointment from an ASP.NET website. I have found the code for sending this <a href="http://msdn.microsoft.com/en-us/library/bb655909%28office.12%29.aspx" rel="noreferrer">here</a>, and tried to implement it. But for some unknown reason it is not working properly.</p>
  
  <p>My server onto which the code is running is in US/Central timezone. I want to send this appointment to clients who are in London. So there are a Daylight savings issue here, which need to be resolved.</p>
  
  <p>I haven't found any understandable explanation about the strings that are making up the appointment. I think the timezone issue could be resolved with <code>TZOFFSETFROM</code> and <code>TZOFFSETTO</code>, but since I don't know how these things work, I couldn't understand what to do.</p>
  
  <p>Can someone please explain those things in plain English?</p>
  
  <p><strong>Edit</strong></p>
  
  <p>Here is the portion of the string that are being used to calculate the timezone - </p>
  
  <pre><code>string timezone = "BEGIN:VTIMEZONE"
                    + "\r\n" + "TZID:US/Central"
                    + "\r\n" + "X-MICROSOFT-CDO-TZID:11" 
                    + "\r\n" + "BEGIN:STANDARD"
                    + "\r\n" + "DTSTART:16010101T020000" 
                    + "\r\n" + "TZOFFSETFROM:-0500"
                    + "\r\n" + "TZOFFSETTO:-0600" 
                    + "\r\n" + "RRULE:FREQ=YEARLY;WKST=MO;INTERVAL=1;BYMONTH=11;BYDAY=1SU"
                    + "\r\n" + "END:STANDARD" 
                    + "\r\n" + "BEGIN:DAYLIGHT" 
                    + "\r\n" + "DTSTART:16010101T020000" 
                    + "\r\n" + "TZOFFSETFROM:-0600"
                    + "\r\n" + "TZOFFSETTO:-0500" 
                    + "\r\n" + "RRULE:FREQ=YEARLY;WKST=MO;INTERVAL=1;BYMONTH=3;BYDAY=2SU"
                    + "\r\n" + "END:DAYLIGHT"
                    + "\r\n" + "END:VTIMEZONE";
  </code></pre>
  
  <p>Here these two attributes(I don't exactly know their type name, so I am using "attributes" to point to them. My apologies) are used in two places, first after <code>BEGIN:STANDARD</code> and after <code>BEGIN:DAYLIGHT</code>. Why? If I specify a start date of <code>DTSTART;TZID=US/Central:20101006T100000Z</code> in the <code>BEGIN:VEVENT</code> block, what time it would show at client's outlook who is in London?</p>
  
  <p><strong>Second Edit</strong><br />
  OK, I now understand that this <code>VTIMEZONE</code> defines a specific timezone. After specifying a timezone I need to specify a time for the calender in the <code>VEVENT</code> section, which is <code>DTSTART;TZID=US/Central:20100101T100000</code>. Now should this time be current time? I mean, when specifying a time should I consider daylight saving, or just get the current time from that timezone and use it there?</p>
  
  <p><strong>Third Edit</strong></p>
  
  <p>What time should I specify in the following block - </p>
  
  <pre><code>string event = "BEGIN:VEVENT" 
                 + "\r\n" + "DTSTAMP:{8}"             
                 + "\r\n" + "DTSTART;TZID=US/Central:{0}"  // What time should I specify here? 
                 + "\r\n" + "SUMMARY:{7}"
                 .................
  </code></pre>
  
  <p>Should I consider daylight savings when specifying <code>DTSTART</code>, or should I always specify standard time and it will be automatically adjusted for daylight savings?</p>