Gmail runs TLS/SSL secured POP3 server on pop.gmail.com, port 995. The following C# code demonstrates how to connect to it using Rebex Secure Mail or Rebex Secure POP3:
// connect and log in
Pop3 client = new Pop3();
client.Connect("pop.gmail.com", 995, null, Pop3Security.Implicit);
client.Login(email, password);
// process messagess...
// logount and disconnect
client.Disconnect();
For a complete example, see the following blogpost HOWTO: Download emails from a GMail account in C#