.NET comes with some new and interesting toys, but the one thing that is missing
the ability to receive POP3 Mail. Here we will build a class to take care of
this oversight.

Logging On & Logging Off

Here is the code to connect to the server and communicate with it; also, it
allows you to perform the two most basic mail functions, which are Logging On
and Logging Off.

If you check the code you will notice that when responses are checked to be okay we only check
for the +OK, other information maybe returned after but this is not part of the
standard and should be ignored.

Once you have logged in the next easiest thing to do is retrieve statistics
about the mailbox and messages.

You will find the POP3 class code with three new properties MailBoxSize,
MessageCount, and a new class MailMessage. Although now it only holds the ID
and size, we fill go on to add more properties as we retrieve them from the
server.

If you check the code you can see in the code that the MailBoxSize and MessageCount properties have
been written to set the value the first time they are called, this has been
done to reduce unnecessary traffic. Your mailbox will locked once you have
logged in and not released until you log out, so remember the quicker you
perform your task the better. If you wish to experiment remember that if your
code bombs out whilst you are logged into your mailbox it will remain locked
until it times out.

So now, you have the ability to add a “You’ve got mail!” component to you
homepage, or better identify oversized emails in your mailbox.

Now we shall look into retrieving the mail message from the server, and then go
on to extract the header information.

If you check the code you can see that we have now modified the MailMessage Class.

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        Public Class MailMessage
            Inherits System.Web.Mail.MailMessage

The class now inherits from the SMTP MailMessage class. This means that it now
can hold all the information of the email without us having to re-invent the
wheel; it also makes it easy to pass the mail back out using the SMTP Mail
class.

Now that we are going to be retrieving the entire message, we can expect to
receive a lot more data. The Getdata function has been enhanced to be able to
read more than just a short reply.

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        Private Function getData() As String
            Dim bData(t.ReceiveBufferSize) As Byte
            getData = ""
            Do
                'get the data
                s.Read(bData, 0, bData.Length)
                getData += System.Text.Encoding.ASCII.GetString(bData)
                'clear byte array for next pass
                bData.Clear(bData, 0, bData.Length)
                'wait for the dataavailble flag to get set
                System.Threading.Thread.Sleep(250)
                'if there is more data repeat
            Loop While s.DataAvailable
        End Function

The message stream is read in a loop until there is no more data. There is a
small delay to allow the DataAvailable flag to be set, 250 milliseconds seems
more adequate, unless you have anti-virus software that scans emails, in which
you may need to increase this.

There two new public functions in the class, getHeader and getMail. getHeader
uses the TOP pop3 command to retrieve just the header component of the mail
message. Where as getMail uses the RETR pop3 command to retrieve the entire
message and then separates it into its Header and Body parts. Both functions
use the private setHeader function to extract the header information into the
MailMessage.

The setHeader function extracts the standard header information and a few of the
more useful ones such as Message-ID. The mail Header and does contain a lot
more information, as to whether is useful is up to you.

Deleting messages is a simple but important task; here you will see the
GetHeader function being used to create a list of Messages to be marked for
deletion by the delete function.

The delete function uses the DELE pop3 command to delete a mail by using the
message number, this may be a problem. In a web situation once the list has
been produced there could be some time until a selection is made. If this is
the case the message cannot be guaranteed to be in the same position, as there
is the possibility that the MailBox may have be accessed by another client.

This being the case, the example uses the Message-ID header value to identify
the message uniquely. It does mean however that we have to search for the
message number. This is easily done in the loop that is used to produce the
list, if a match is found the message is deleted and the list item struck out
to indicate this.

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                    'check wether the mail has been marked for deletion
                    If Request.Form.Item(ma(cnt).Headers("Message-ID")) <> "" Then
                        'if it has, delete it a indicate its deletion.
                        If p.delete(ma(cnt)) Then
                            r.Font.Strikeout = True
                        End If
                    End If