Respond to a meeting request item

The downloaded e-mail message containing the meeting request item is an ordinary message with extra body part of "text/calendar" content-type.

Thus, you download such messages as any others:

C#

// Download entire message from the server.
MailMessage msg = pop.DownloadEntireMessage(1);

VB.NET

' Download entire message from the server.
Dim msg As MailMessage =  pop.DownloadEntireMessage(1)

To make your application aware of meeting request items, you should check each incoming message for vCalendar events:

C#

// Make sure this message is vCalendar event 
if (msg.BodyParts["text/calendar"].Text.Length > 0)
{
  calEvent = ParseCalendarRecord(msg.BodyParts["text/calendar"].Text);
}

VB.NET

' Make sure this message is vCalendar event 
If msg.BodyParts("text/calendar").Text.Length > 0 Then
  calEvent = ParseCalendarRecord(msg.BodyParts("text/calendar").Text)
End If

In order to collect all the available information, we need to check as many fields as possible. The category of the calendar item is important, too: if the event denotes a conference, it becomes an appointment in your organizer software. But if it's a meeting request, you should compose and send the meeting confirmation message to the sender. Such reply messages have the same structure as meeting requests, the only difference is in their method field:

C#

// If we accepted the meeting request, generate and send the 
// confirmation message
// ("accepted" in the code below is a boolean whose value was 
// already set accordingly the decision made by the human user).
if (calEvent.method == "REQUEST" && accepted)
{
// The only difference between the request and the reply.
  calEvent.method = "REPLY";

  Smtp mailer = new Smtp();

  // Create message
  mailer.Message.From.Email = "jdoe@domain.com";
  mailer.Message.To.Add(msg.From.Email);
  mailer.Message.Subject = "Meeting Request";

  // Create calendar body
  mailer.Message.BodyParts.Add("text/calendar");
  mailer.Message.BodyParts["text/calendar"].Text = CreateCalendarRecord(calEvent);
  ...
}

VB.NET

' If we accepted the meeting request, generate and send the 
' confirmation message
' ("accepted" in the code below is a boolean whose value was 
' already set accordingly the decision made by the human user).
If calEvent.method = "REQUEST" And accepted Then
' The only difference between the request and the reply.
  calEvent.method = "REPLY"
 
  Dim mailer As New Smtp() 
 
  ' Create message
  mailer.Message.From.Email = "jdoe@domain.com"
  mailer.Message.To.Add(msg.From.Email)
  mailer.Message.Subject = "Meeting Request"
 
  ' Create calendar body
  mailer.Message.BodyParts.Add("text/calendar")
  mailer.Message.BodyParts("text/calendar").Text = CreateCalendarRecord(calEvent)
  ...
End If

After creating the vCalendar event, the message can be sent through SMTP server.

Code example:

The sample code below receives a message and analyzes it for vCalendar content. If the message is a meeting request, a confirmation message is sent to the sender. The sample also displays the vCalendar part of the message.

C#

public struct VCalendar 
{
    public int year, month, day, hour, minute, second, duration;
    public string summary, location, method;
}

string CreateCalendarRecord(VCalendar calEvent)
{
    string calRecord;
    calRecord  = "BEGIN:VCalendar" + "\r\n";
    calRecord += "METHOD:" + calEvent.method + "\r\n";
    calRecord += "BEGIN:VEVENT" + "\r\n";
    calRecord += "DTSTART:" + calEvent.year.ToString("0000") + calEvent.month.ToString("00") + calEvent.day.ToString("00");

    calRecord += "T" + calEvent.hour.ToString("00") + calEvent.minute.ToString("00") + calEvent.second.ToString("00") + "Z\r\n";

    calEvent.hour += calEvent.duration;
    calRecord += "DTEND:" + calEvent.year.ToString("0000") + calEvent.month.ToString("00") + calEvent.day.ToString("00");

    calRecord += "T" + calEvent.hour.ToString("00") + calEvent.minute.ToString("00") + calEvent.second.ToString("00") + "Z\r\n";

    calRecord += "LOCATION:" + calEvent.location + "\r\n";
    calRecord += "SUMMARY:" + calEvent.summary+ "\r\n";
    calRecord += "END:VEVENT" + "\r\n";
    calRecord += "END:VCalendar";
    return calRecord;
}

VCalendar ParseCalendarRecord(string msg_string)
{
    VCalendar calEvent = new VCalendar();
    string [] lines = null;
    int delimiterIdx;

    string start_time;
    string keyName, keyValue;

    // Split text on lines 
    lines = msg_string.Split('\n');

    // Iterate thorough all lines
    for (int i = 0; i < lines.Length; i++)
    {
        delimiterIdx = lines[i].IndexOf(":");

        // If delimiter ':' char is found
        if (delimiterIdx > 0)
        {
            // First part of the line is the required name 
            keyName = lines[i].Substring(0, delimiterIdx);

            // To the right from delimiter is the value
            keyValue = lines[i].Substring(delimiterIdx + 1, lines[i].Length - delimiterIdx - 2);

            // If next string begins with space - append it to description
            while (i + 1 < lines.Length)
            {
                if (lines[i + 1][0] == ' ')
                {
                    i++;
                    keyValue += lines[i].Substring(1, lines[i].Length - 2);
                }
                else break;
            }

            // Parse defenitions 
            switch(keyName)
            {
                case "METHOD": 
                    calEvent.method = keyValue;
                    break;
                case "DTSTART": 
                    start_time = keyValue;
                    calEvent.year = int.Parse(start_time.Substring(0,4));
                    calEvent.month = int.Parse(start_time.Substring(4,2));
                    calEvent.day = int.Parse(start_time.Substring(6,2));
                    calEvent.hour = int.Parse(start_time.Substring(9,2));
                    calEvent.minute = int.Parse(start_time.Substring(11,2));
                    calEvent.second = int.Parse(start_time.Substring(13,2));
                    break;
                case "LOCATION": 
                    calEvent.location = keyValue;
                    break;
                case "SUMMARY" : 
                    calEvent.summary = keyValue;
                    break;
                default:
                    break;
            }
        }
    }

    return calEvent;
}

Pop3 pop = new Pop3();

// Connect to POP3 server
pop.Connect("mail.domain.com");
pop.Login("jdoe","secret");

// Download entire message from the server.
MailMessage msg = pop.DownloadEntireMessage(1);

// Disconnect from POP3 server
pop.Disconnect();

VCalendar calEvent = new VCalendar();

bool isVCalItem = false;

// Make sure that this message is vCalendar event 
if (msg.BodyParts["text/calendar"].Text.Length > 0)
{
    calEvent = ParseCalendarRecord(msg.BodyParts["text/calendar"].Text);
    isVCalItem = true;
}

// This flag indicates whether the request was accepted or not.
// Let's assume the human user decided to accept this meeting request.
bool accepted = true;

// If request accepted then generate and send message
if (isVCalItem && calEvent.method == "REQUEST" && accepted)
{
    calEvent.method = "REPLY";

    Smtp mailer = new Smtp();

    // Create message
    mailer.Message.From.Email = "jdoe@domain.com";
    mailer.Message.To.Add(msg.From.Email);
    mailer.Message.Subject = "Meeting Request";

    // Create calendar body
    mailer.Message.BodyParts.Add("text/calendar");
    mailer.Message.BodyParts["text/calendar"].Text = CreateCalendarRecord(calEvent);

    // Connect to SMTP server and send meeting request
    mailer.SmtpServers.Add("mail.domain.com", "jdoe", "secret");
    mailer.Send();
}

VB.NET

Public Structure VCalendar
    Public year As Integer,month As Integer,day As Integer,hour As Integer,minute As Integer,second As Integer,duration As Integer
    Public summary As String,location As String,method As String
End Structure
 
Private Function CreateCalendarRecord(ByVal calEvent As VCalendar) As String
    Dim calRecord As String
    calRecord  = "BEGIN:VCalendar" + "\r\n"
    calRecord += "METHOD:" + calEvent.method + "\r\n"
    calRecord += "BEGIN:VEVENT" + "\r\n"
    calRecord += "DTSTART:" + calEvent.year.ToString("0000") + calEvent.month.ToString("00") + calEvent.day.ToString("00")
 
    calRecord += "T" + calEvent.hour.ToString("00") + calEvent.minute.ToString("00") + calEvent.second.ToString("00") + "Z\r\n"
 
    calEvent.hour += calEvent.duration
    calRecord += "DTEND:" + calEvent.year.ToString("0000") + calEvent.month.ToString("00") + calEvent.day.ToString("00")
 
    calRecord += "T" + calEvent.hour.ToString("00") + calEvent.minute.ToString("00") + calEvent.second.ToString("00") + "Z\r\n"
 
    calRecord += "LOCATION:" + calEvent.location + "\r\n"
    calRecord += "SUMMARY:" + calEvent.summary+ "\r\n"
    calRecord += "END:VEVENT" + "\r\n"
    calRecord += "END:VCalendar"
    Return calRecord
End Function
 
Private Function ParseCalendarRecord(ByVal msg_string As String) As VCalendar
    Dim calEvent As New VCalendar() 
    Dim lines() As String =  Nothing 
    Dim delimiterIdx As Integer
 
    Dim start_time As String
    Dim keyName As String,keyValue As String
 
    ' Split text on lines 
    lines = msg_string.Split(vbLf)
 
    ' Iterate thorough all lines
    Dim i As Integer
    For  i = 0 To  lines.Length- 1  Step  i + 1
        delimiterIdx = lines(i).IndexOf(":")
 
        ' If delimiter ':' char is found
        If delimiterIdx > 0 Then
            ' First part of the line is the required name 
            keyName = lines(i).Substring(0, delimiterIdx)
 
            ' To the right from delimiter is the value
            keyValue = lines(i).Substring(delimiterIdx + 1, lines(i).Length - delimiterIdx - 2)
 
            ' If next string begins with space - append it to description
            While i + 1 < lines.Length
                If lines(i + 1)(0) = ' ' Then
                    i = i + 1
                    keyValue += lines(i).Substring(1, lines(i).Length - 2)
                Else
                    Exit While
            End While
 
            ' Parse defenitions 
            Select Case keyName
                Case "METHOD"
                    calEvent.method = keyValue
                Case "DTSTART"
                    start_time = keyValue
                    calEvent.year = Integer.Parse(start_time.Substring(0,4))
                    calEvent.month = Integer.Parse(start_time.Substring(4,2))
                    calEvent.day = Integer.Parse(start_time.Substring(6,2))
                    calEvent.hour = Integer.Parse(start_time.Substring(9,2))
                    calEvent.minute = Integer.Parse(start_time.Substring(11,2))
                    calEvent.second = Integer.Parse(start_time.Substring(13,2))
                Case "LOCATION"
                    calEvent.location = keyValue
                Case "SUMMARY"
                    calEvent.summary = keyValue
                Case Else
            End Select
        End If
    Next
 
    Return calEvent
End Function
 
Dim pop As New Pop3() 
 
' Connect to POP3 server
pop.Connect("mail.domain.com")
pop.Login("jdoe","secret")
 
' Download entire message from the server.
Dim msg As MailMessage =  pop.DownloadEntireMessage(1) 
 
' Disconnect from POP3 server
pop.Disconnect()
 
Dim calEvent As New VCalendar() 
 
Dim isVCalItem As Boolean =  False 
 
' Make sure that this message is vCalendar event 
If msg.BodyParts("text/calendar").Text.Length < 0 Then
    calEvent = ParseCalendarRecord(msg.BodyParts("text/calendar").Text)
    isVCalItem = True
End If
 
' This flag indicates whether the request was accepted or not.
' Let's assume the human user decided to accept this meeting request.
Dim accepted As Boolean =  True 
 
' If request accepted then generate and send message
If isVCalItem And calEvent.method = "REQUEST" And accepted Then
    calEvent.method = "REPLY"
 
    Dim mailer As New Smtp() 
 
    ' Create message
    mailer.Message.From.Email = "jdoe@domain.com"
    mailer.Message.To.Add(msg.From.Email)
    mailer.Message.Subject = "Meeting Request"
 
    ' Create calendar body
    mailer.Message.BodyParts.Add("text/calendar")
    mailer.Message.BodyParts("text/calendar").Text = CreateCalendarRecord(calEvent)
 
    ' Connect to SMTP server and send meeting request
    mailer.SmtpServers.Add("mail.domain.com", "jdoe", "secret")
    mailer.Send()
End If

You can use the same approach to parse calendar entries of other formats (such as iCalendar).