The remote certificate is invalid according to the validation procedure

If you get “The remote certificate is invalid according to the validation procedure” exception while trying to establish SSL connection, most likely your’s server certificate is self-signed.

You can accept self-signed certificates using Mail.dll IMAP POP3 and SMTP client.

First you need to subscribe to ServerCertificateValidate event.
Then you need to create ValidateCertificate method that validates the certificate (ignores certificate chain errors).

The sample below focuses on Imap class but exactly the same steps apply to Pop3 and Smtp classes.

// C# version

using System.Net.Security;
using System;
using Limilabs.Mail;
using Limilabs.Client.IMAP;

internal class Program
{
    private static void Main(string[] args)
    {
        using (Imap client = new Imap())
        {
            // we will use custom validation
            client.ServerCertificateValidate +=
                new ServerCertificateValidateEventHandler(Validate);

            // Minimalistic version to accept any certificate:
            //client.ServerCertificateValidate += (sender, e) => { e.IsValid = true; };

            client.ConnectSSL("server.example.com");
            client.Login("user", "password");

            foreach (long uid in client.GetAll())
            {
                IMail email = new MailBuilder().CreateFromEml(
                    client.GetMessageByUID(uid));
                Console.WriteLine("subject: {0}", email.Subject);
            }

            client.Close();
        }
    }

    private static void Validate(
        object sender,
        ServerCertificateValidateEventArgs e)
    {
        const SslPolicyErrors ignoredErrors =
            SslPolicyErrors.RemoteCertificateChainErrors |
            SslPolicyErrors.RemoteCertificateNameMismatch;

        if ((e.SslPolicyErrors & ~ignoredErrors) == SslPolicyErrors.None)
        {
            e.IsValid = true;
            return;
        }
        e.IsValid = false;
    }

} ;

' VB.NET version

Imports System.Net.Security
Imports System
Imports Limilabs.Mail
Imports Limilabs.Client.IMAP

Public Module Module1

    Public Sub Main(ByVal args As String())
        Using client As New Imap()
            ' we will use custom validation
            AddHandler client.ServerCertificateValidate, AddressOf ValidateCertificate

            client.ConnectSSL("server.example.com")
            client.Login("user", "password")

            For Each uid As Long In client.GetAll()
                Dim email As IMail = New MailBuilder().CreateFromEml(client.GetMessageByUID(uid))
                Console.WriteLine("subject: {0}", email.Subject)
            Next

            client.Close()
        End Using
    End Sub

    Private Sub ValidateCertificate( _
       ByVal sender As Object, _
       ByVal e As ServerCertificateValidateEventArgs)

       Const ignoredErrors As SslPolicyErrors = _
           SslPolicyErrors.RemoteCertificateChainErrors Or _
           SslPolicyErrors.RemoteCertificateNameMismatch

        If (e.SslPolicyErrors And Not ignoredErrors) = SslPolicyErrors.None Then
           e.IsValid = True
           Return
        End If
        e.IsValid = False
    End Sub

End Module

Tags: C#, IMAP, Mail.dll, POP3, SMTP, SSL, VB.NET

This entry was posted on Monday, October 25th, 2010 at 15:44 and is filed under Component. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.