Introduction
in this article, I'll show you how to retrieve mail from POP server based on RFC 1725.
Algorithm for Retrieving Mail
to retrieve mail from POP server, I just follow rule of RFC 1725. You also can download that paper (RFC 1725).
here's the algorithm:
Client : +OK Server POP Ready!!
Client : USER xxx
Server : +OK
Client : PASS yyy
Server : +OK user successfully logged on
Client : STAT
Server : +OK n m
Client : RETR 1
Server : +OK
---{ data }-----
Client : QUIT
Server : +OK Server POP signing off
Implementation
it's easy to implement an application if we know the algorithm to retrieve mail from a POP server. In this article, I use the TcpClient and NetworkStream classes. Firstly, declare public variables:
public TcpClient Server;
public NetworkStream NetStrm;
public StreamReader RdStrm;
public string Data;
public byte[] szData;
public string CRLF = "\r\n";
here's the code for when the Connect Button is clicked:
private void ConnectBtn_Click(object sender, System.EventArgs e)
{
// change cursor into wait cursor
Cursor cr = Cursor.Current;
Cursor.Current = Cursors.WaitCursor;
// create server POP3 with port 110
Server = new TcpClient(POPServ.Text,110);
Status.Items.Clear();
try
{
// initialization
NetStrm = Server.GetStream();
RdStrm= new StreamReader(Server.GetStream());
Status.Items.Add(RdStrm.ReadLine());
// Login Process
Data = "USER "+ User.Text+CRLF;
szData = System.Text.Encoding.ASCII.GetBytes(Data.ToCharArray());
NetStrm.Write(szData,0,szData.Length);
Status.Items.Add(RdStrm.ReadLine());
Data = "PASS "+ Passw.Text+CRLF;
szData = System.Text.Encoding.ASCII.GetBytes(Data.ToCharArray());
NetStrm.Write(szData,0,szData.Length);
Status.Items.Add(RdStrm.ReadLine());
// Send STAT command to get information ie: number of mail and size
Data = "STAT"+CRLF;
szData = System.Text.Encoding.ASCII.GetBytes(Data.ToCharArray());
NetStrm.Write(szData,0,szData.Length);
Status.Items.Add(RdStrm.ReadLine());
// change enabled - disabled button
ConnectBtn.Enabled = false;
DisconnectBtn.Enabled = true;
RetrieveBtn.Enabled = true;
// back to normal cursor
Cursor.Current = cr;
}
catch(InvalidOperationException err)
{
Status.Items.Add("Error: "+err.ToString());
}
}
here's the code for when the Disconnect Button is clicked:
private void DisconnectBtn_Click(object sender, System.EventArgs e)
{
// change cursor into wait cursor
Cursor cr = Cursor.Current;
Cursor.Current = Cursors.WaitCursor;
// Send QUIT command to close session from POP server
Data = "QUIT"+CRLF;
szData = System.Text.Encoding.ASCII.GetBytes(Data.ToCharArray());
NetStrm.Write(szData,0,szData.Length);
Status.Items.Add(RdStrm.ReadLine());
//close connection
NetStrm.Close();
RdStrm.Close();
// change enabled - disabled button
ConnectBtn.Enabled = true;
DisconnectBtn.Enabled = false;
RetrieveBtn.Enabled = false;
// back to normal cursor
Cursor.Current = cr;
}
here's code when Retrieve Button clicked:
private void RetrieveBtn_Click(object sender, System.EventArgs e)
{
// change cursor into wait cursor
Cursor cr = Cursor.Current;
Cursor.Current = Cursors.WaitCursor;
string szTemp;
Message.Clear();
try
{
// retrieve mail with number mail parameter
Data = "RETR "+ Number.Text+CRLF;
szData = System.Text.Encoding.ASCII.GetBytes(Data.ToCharArray());
NetStrm.Write(szData,0,szData.Length);
szTemp = RdStrm.ReadLine();
if(szTemp[0]!='-')
{
while(szTemp!=".")
{
Message.Text += szTemp;
szTemp = RdStrm.ReadLine();
}
}
else
{
Status.Items.Add(szTemp);
}
// back to normal cursor
Cursor.Current = cr;
}
catch(InvalidOperationException err)
{
Status.Items.Add("Error: "+err.ToString());
}
}
Testing
build and run this project. Set the POP server, user and password. After that you'll get a response message from the POP server (you can see on status box) ie: +OK 2 624 if success or -ERR if fail. The words "+OK 2 624" mean you have two emails and total size 624.
now, you can set the mail message number and then click Retrieve button. Then you'll get the mail according to the mail number that you wrote on Mail Number Box.
