This is Gmail link that points to certain conversation:

“13216515baefe747″ is the Gmail thread-ID in hex.

Here’s the code that:

1. Selects “All Mail” folder
2. Gets the newest message UID
3. Obtains Gmail thread ID for this message (X-GM-THRID)
4. Converts it to hex
5. Creates the url that point to the Gmail conversation

// C# version

using (Imap client = new Imap())
{
    client.ConnectSSL("imap.gmail.com");
    client.Login("pat@gmail.com", "password");

    // select "All Mail" folder
    List<FolderInfo> allFolders = client.GetFolders();
    FolderInfo allMail = new CommonFolders(allFolders).AllMail;
    client.Select(allMail);

    // get IMAP uid of the newest message
    long lastUid = client.GetAll().Last();

    // get message info
    MessageInfo info = client.GetMessageInfoByUID(lastUid);

    // extract Gmail thread ID
    Int64 threadId = Int64.Parse(info.Envelope.GmailThreadId);
    string threadIdAsHex = threadId.ToString"X");

    // create url
    string url = string.Format(
        "https://mail.google.com/mail/u/0/#inbox/{0}",
        threadIdAsHex);

    Console.WriteLine(url);

    client.Close();
}

' VB.NET version

Using client As New Imap()
	client.ConnectSSL("imap.gmail.com")
	client.Login("pat@gmail.com", "password")

	' select "All Mail" folder
	Dim allFolders As List(Of FolderInfo) = client.GetFolders()
	Dim allMail As FolderInfo = New CommonFolders(allFolders).AllMail
	client.[Select](allMail)

	' get IMAP uid of the newest message
	Dim lastUid As Long = client.GetAll().Last()

	' get message info
	Dim info As MessageInfo = client.GetMessageInfoByUID(lastUid)

	' extract Gmail thread ID
	Dim threadId As Int64 = Int64.Parse(info.Envelope.GmailThreadId)
	Dim threadIdAsHex As String = threadId.ToString("X")

	' create url
	Dim url As String = String.Format( _
		"https://mail.google.com/mail/u/0/#inbox/{0}", _
		threadIdAsHex)

	Console.WriteLine(url)

	client.Close()
End Using

Here you can find some more information about how to search by X-GM-THRID and all other Gmail IMAP extensions.

Here’s the list of Gmail IMAP protocol extensions implemented in Mail.dll:

• Extension of the LIST command: XLIST
• Extension of the SEARCH command: X-GM-RAW
• Access to the Gmail unique message ID: X-GM-MSGID
• Access to the Gmail thread ID: X-GM-THRID
• Access to Gmail labels: X-GM-LABELS

You can read on how to use Mail.dll with Gmail in the following articles:

• Get Gmail thread id
• Search Gmail thread id
• Get Gmail message id
• Search Gmail message id
• Get Gmail labels for specified messages
• Label message with Gmail label
• Search Gmail label
• Localized Gmail IMAP Folders
• Search Gmail using Gmail’s search syntax
• Create Gmail url-ID via IMAP

Gmail treats labels as folders for the purposes of IMAP.

As such, labels can be modified using the standard IMAP commands, CreateFolder, RenameFolder, and DeleteFolder, that act on folders.

System labels, which are labels created by Gmail, are reserved and prefixed by “[Gmail]” or “[GoogleMail]” in the list of labels.

Use the XLIST command to get the entire list of labels for a mailbox.

The labels for a given message may be retrieved by using the X-GM-LABELS attribute with the FETCH command.

It is also possible to use the X-GM-LABELS attribute to return the UIDs for all messages with a given label, using the SEARCH command.

// C# version

using (Imap imap = new Imap())
{
    imap.ConnectSSL("imap.gmail.com");
    imap.Login("pat@gmail.com", "password");

    imap.SelectInbox();

    List<long> uids = imap.Search().Where(
        Expression.GmailLabel("MyLabel"));

    foreach (MessageInfo info in imap.GetMessageInfoByUID(uids))
    {
        Console.WriteLine("{0} - {1}",
            info.Envelope.GmailThreadId,
            info.Envelope.Subject);
    }

    imap.Close();
}

' VB.NET version

Using imap As New Imap()
	imap.ConnectSSL("imap.gmail.com")
	imap.Login("pat@gmail.com", "password")

	imap.SelectInbox()

	Dim uids As List(Of Long) = imap.Search().Where(Expression.GmailLabel("MyLabel"))

	For Each info As MessageInfo In imap.GetMessageInfoByUID(uids)
            Console.WriteLine("{0} - {1}",  _
                info.Envelope.GmailThreadId,  _
                info.Envelope.Subject)
	Next

	imap.Close()
End Using

You can learn more about this Gmail IMAP extension here:
http://code.google.com/apis/gmail/imap/#x-gm-labels

Gmail treats labels as folders for the purposes of IMAP.

As such, labels can be modified using the standard IMAP commands, CreateFolder, RenameFolder, and DeleteFolder, that act on folders.

System labels, which are labels created by Gmail, are reserved and prefixed by “[Gmail]” or “[GoogleMail]” in the list of labels.

Use the XLIST command to get the entire list of labels for a mailbox.

The labels for a given message may be retrieved by using the X-GM-LABELS attribute with the FETCH command.

Labels may be added to a message using the STORE command in conjunction with the X-GM-LABELS attribute.

// C# version

using (Imap imap = new Imap())
{
    imap.ConnectSSL("imap.gmail.com");
    imap.Login("pat@gmail.com", "password");

    imap.SelectInbox();
    long uid = imap.GetAll().Last();

    imap.GmailLabelMessageByUID(uid, "MyLabel");

    List<string> labels = imap.GmailGetLabelsByUID(uid);
    labels.ForEach(Console.WriteLine);

    imap.Close();
}

' VB.NET version

Using imap As New Imap()
	imap.ConnectSSL("imap.gmail.com")
	imap.Login("pat@gmail.com", "password")

	imap.SelectInbox()
	Dim uid As Long = imap.GetAll().Last()

	imap.GmailLabelMessageByUID(uid, "MyLabel")

	Dim labels As List(Of String) = imap.GmailGetLabelsByUID(uid)
	labels.ForEach(Console.WriteLine)

	imap.Close()
End Using

You can learn more about this Gmail IMAP extension here:
http://code.google.com/apis/gmail/imap/#x-gm-labels

Gmail treats labels as folders for the purposes of IMAP.

As such, labels can be modified using the standard IMAP commands, CreateFolder, RenameFolder, and DeleteFolder, that act on folders.

System labels, which are labels created by Gmail, are reserved and prefixed by “[Gmail]” or “[GoogleMail]” in the list of labels.

Use the XLIST command to get the entire list of labels for a mailbox.

The labels for a given message may be retrieved by using the X-GM-LABELS attribute with the FETCH command.

For list of messages

// C# version

using (Imap imap = new Imap())
{
    imap.ConnectSSL("imap.gmail.com");
    imap.Login("pat@gmail.com", "password");

    imap.SelectInbox();

    List<long> uids = imap.GetAll();
    List<MessageInfo> infos = imap.GetMessageInfoByUID(uids);

    foreach (MessageInfo info in infos)
    {
        List<string> labels = info.GmailLabels.Labels;

        Console.WriteLine("[{0}] {1}",
            string.Join(" ", labels.ToArray()),
            info.Envelope.Subject);
    }

    imap.Close();
}

' VB.NET version

Using imap As New Imap()
	imap.ConnectSSL("imap.gmail.com")
	imap.Login("pat@gmail.com", "password")

	imap.SelectInbox()

	Dim uids As List(Of Long) = imap.GetAll()
	Dim infos As List(Of MessageInfo) = imap.GetMessageInfoByUID(uids)

	For Each info As MessageInfo In infos
            Dim labels As List(Of String) = info.GmailLabels.Labels

	    Console.WriteLine("[{0}] {1}",  _
                String.Join(" ", labels.ToArray()),  _
                info.Envelope.Subject)
	Next

	imap.Close()
End Using

For single message:

// C# version

using (Imap imap = new Imap())
{
    imap.ConnectSSL("imap.gmail.com");
    imap.Login("pat@gmail.com", "password");

    imap.SelectInbox();

    long uid = imap.GetAll().Last();
    List<string> labels = imap.GmailGetLabelsByUID(uid);

    labels.ForEach(Console.WriteLine);

    imap.Close();
}

' VB.NET version

Using imap As New Imap()
	imap.ConnectSSL("imap.gmail.com")
	imap.Login("pat@gmail.com", "password")

	imap.SelectInbox()

	Dim uid As Long = imap.GetAll().Last()
	Dim labels As List(Of String) = imap.GmailGetLabelsByUID(uid)

	labels.ForEach(Console.WriteLine)

	imap.Close()
End Using

You can learn more about this Gmail IMAP extension here:
http://code.google.com/apis/gmail/imap/#x-gm-labels