(VB.NET) Reading Unread POP3 Email

The POP3 protocol cannot determine which emails are "unread," and pure POP3 servers do not store this information. Servers like Exchange Server, offering both POP3 and IMAP interfaces, do contain read/unread data, but it's only accessible through IMAP. Email clients like Outlook and Thunderbird store read/unread statuses on the client side. The example demonstrates using UIDLs to track and manage "unread" emails.

Note: This example requires Chilkat v11.0.0 or greater.

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Dim success As Boolean = False

' This example requires the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.

' The mailman object is used for receiving (POP3) 
' and sending (SMTP) email.
Dim mailman As New Chilkat.MailMan

' Set the POP3 server's hostname
mailman.MailHost = "pop.example.com"

' Set the POP3 login/password.
mailman.PopUsername = "***"
mailman.PopPassword = "***"

' Keep a records of already-seen UIDLs in hash table serialized to an XML file.
Dim seenUidlsPath As String = "c:/temp/seenUidls.xml"

Dim sbXml As New Chilkat.StringBuilder
Dim htSeenUidls As New Chilkat.Hashtable
Dim fac As New Chilkat.FileAccess
If (fac.FileExists(seenUidlsPath) = True) Then
    success = sbXml.LoadFile(seenUidlsPath,"utf-8")
    If (success = False) Then
        Debug.WriteLine(sbXml.LastErrorText)
        Exit Sub
    End If

    htSeenUidls.AddFromXmlSb(sbXml)
End If


' Get the complete list of UIDLs on the mail server.
Dim stUidls As New Chilkat.StringTable
success = mailman.FetchUidls(stUidls)
If (success = False) Then
    Debug.WriteLine(mailman.LastErrorText)
    Exit Sub
End If


' Build a list of unseen UIDLs
Dim stUnseenUidls As New Chilkat.StringTable

Dim uidl As String
Dim i As Integer = 0
Dim count As Integer = stUidls.Count
While i < count
    uidl = stUidls.StringAt(i)
    If (htSeenUidls.Contains(uidl) <> True) Then
        stUnseenUidls.Append(uidl)
    End If

    i = i + 1
End While

If (stUnseenUidls.Count = 0) Then
    Debug.WriteLine("No unseen emails!")
    Exit Sub
End If


' Download the unseen emails, adding each UIDL to the "seen" hash table.
Dim email As New Chilkat.Email

count = stUnseenUidls.Count
i = 0
While i < count
    ' Download the full email.
    uidl = stUnseenUidls.StringAt(i)
    success = mailman.FetchByUidl(uidl,False,0,email)
    If (success = False) Then
        Debug.WriteLine(mailman.LastErrorText)
        Exit Sub
    End If


    Debug.WriteLine(i)
    Debug.WriteLine("From: " & email.From)
    Debug.WriteLine("Subject: " & email.Subject)

    ' Add this UIDL to the "seen" hash table.
    htSeenUidls.AddStr(uidl,"")

    i = i + 1
End While

mailman.Pop3EndSession()

' Update the "seen" UIDLs file.
sbXml.Clear()
htSeenUidls.ToXmlSb(sbXml)
success = sbXml.WriteFile(seenUidlsPath,"utf-8",False)
If (success = False) Then
    Debug.WriteLine(sbXml.LastErrorText)
    Exit Sub
End If


Debug.WriteLine("Success.")