You can use Mail.dll to easy reply to an HTML and plain-text emails.

ReplyBuilder class allows you to specify custom HTML and plain-text reply templates. Mail.dll will parse HTML, extract body part, and build-in template engine will do the rest to create nicely formatted reply with all attachments, To and Cc fields set.

The next great thing is that plain-text version of the email is generated automatically.

You can also take advantage of ReplyAll method that makes it easy to reply to all: senders of the message and all To and Cc recipients

In our example we’ll use Mail.dll IMAP client to download first message from an IMAP server. Then we’ll use ReplyBuilder to create a reply email message. Finally we’ll use Mail.dll SMTP client to send this message.

// C#

IMail original = GetFirstMessage();

ReplyBuilder replyBuilder = original.Reply();
// You can specify your own custom template:
replyBuilder.HtmlReplyTemplate =
    "[Html]" +
    "<br /><br />" +
    "On [Original.Date] [Original.Sender.Name] wrote:" +
    "<blockquote " +
        "style='margin-left: 1em; " +
        "padding-left: 1em; " +
        "border-left: 1px #ccc solid;'>" +
    "[QuoteHtml]" +
    "</blockquote>";

replyBuilder.Html =
    "Alice, <br/><br/>thanks for your email.";

MailBuilder builder = replyBuilder.ReplyToAll(
    new MailBox("bob@example.org", "Bob"));

// You can add attachments to your reply
//builder.AddAttachment("report.csv");

IMail reply = builder.Create();

using (Smtp smtp = new Smtp())
{
    smtp.Connect("smtp.example.com"); // or ConnectSSL
    smtp.UseBestLogin("user", "password");
    smtp.SendMessage(reply);
    smtp.Close();
}

static IMail GetFirstMessage()
{
    IMail email;
    using (Imap imap = new Imap())
    {
        imap.Connect("imap.example.com"); // or ConnectSSL if you want to use SSL
        imap.UseBestLogin("user", "password");
        List<long> uids = imap.GetAll();
        if (uids.Count == 0)
            throw new Exception("There are no messages");
        string eml = imap.GetMessageByUID(uids[0]);
        email = new MailBuilder().CreateFromEml(eml);
        imap.Close();
    }
    return email;
}

' VB.NET

Dim original As IMail = GetFirstMessage()

Dim replyBuilder As ReplyBuilder = original.Reply()

' You can specify your own custom template:
replyBuilder.HtmlReplyTemplate = _
    "[Html]" + _
    "<br /><br />" + _
    "On [Original.Date] [Original.Sender.Name] wrote:" + _
    "<blockquote " + _
        "style='margin-left: 1em; " + _
        "padding-left: 1em; " + _
        "border-left: 1px #ccc solid;'>" + _
    "[QuoteHtml]" + _
    "</blockquote>"

replyBuilder.Html = _
    "Alice, <br/><br/>thanks for your email."

Dim builder As MailBuilder = replyBuilder.ReplyToAll( _
    New MailBox("bob@example.org", "Bob"))

' You can add attachments to your reply
'builder.AddAttachment("report.csv")

Dim reply As IMail = builder.Create()

Using smtp As New Smtp()
	smtp.Connect("smtp.example.com") ' or ConnectSSL
	smtp.UseBestLogin("user", "password")
	smtp.SendMessage(reply)
	smtp.Close()
End Using

Private Shared Function GetFirstMessage() As IMail
	Dim email As IMail
	Using imap As New Imap()
		imap.Connect("imap.example.com")
		' or ConnectSSL if you want to use SSL
		imap.UseBestLogin("user", "password")
		Dim uids As List(Of Long) = imap.GetAll()
		If uids.Count = 0 Then
			Throw New Exception("There are no messages")
		End If
		Dim eml As String = imap.GetMessageByUID(uids(0))
		email = New MailBuilder().CreateFromEml(eml)
		imap.Close()
	End Using
	Return email
End Function

Mail.dll MIME and email API’s may be used to get the plain-text body and HTML body from an email message.

If a message contains plain-text, no conversion is necessary. It’s simply a matter of using the Text property of IMail interface.

If however the email does not contain plain-text and only HTML content is available, GetTextFromHtml method may be used to convert the HTML to plain-text.

The internal conversion process is much more sophisticated than what can be accomplished with the simple regular-expression code. Converting HTML to plain text is much more than simply removing HTML tags from an HTML document.

Mail.dll contains full-blown HTML parser that handles script tags, comments, CDATA and even incorrect HTML.

The following C# and VB.NET code extracts plain-text from the HTML body of the email message:

// C#

IMail email = ...

string text = "";
if (email.IsText)
    text = email.Text;
else if (email.IsHtml)
    text = email.GetTextFromHtml();
Console.WriteLine(text);

' VB.NET

Dim email As IMail = ...

Dim text As String = ""
If email.IsText Then
    text = email.Text
ElseIf email.IsHtml Then
    text = email.GetTextFromHtml()
End If
Console.WriteLine(text)

You can also use GetBodyAsText method that returns body in plain text format (it uses IMail.Text property or GetTextFromHtml method).

// C#

IMail email = ...

string text = email.GetBodyAsText();
Console.WriteLine(text);

' VB.NET

Dim email As IMail = ...

Dim text As String = email.GetBodyAsText()
Console.WriteLine(text)

The easiest way is to use BCC field (Blind-Carbon-Copy),  and specify Undisclosed recipients group as the message recipient.

// C# version

MailBuilder builder = new MailBuilder();
builder.From.Add(new MailBox("alice@example.com", "Alice"));
builder.To.Add(new MailGroup("Undisclosed recipients"));

builder.Bcc.Add(new MailBox("bob@example.com", "Bob"));
builder.Bcc.Add(new MailBox("tom@example.com", "Tom"));
builder.Bcc.Add(new MailBox("john@example.com", "John"));

builder.Subject = "Put subject here";
builder.Html = "Put <strong>HTML</strong> message here.";

// Plain text is automatically generated, but you can change it:
//builder.Text = "Put plain text message here.";

IMail email = builder.Create();

// Send the message
using (Smtp smtp = new Smtp())
{
    smtp.Connect("server.example.com");   // or ConnectSSL for SSL
    smtp.UseBestLogin("user", "password"); // remove if not needed

    smtp.SendMessage(email);

    smtp.Close();
}

' VB.NET version

Dim builder As New MailBuilder()
builder.From.Add(New MailBox("alice@example.com", "Alice"))
builder.[To].Add(New MailGroup("Undisclosed recipients"))

builder.Bcc.Add(New MailBox("bob@example.com", "Bob"))
builder.Bcc.Add(New MailBox("tom@example.com", "Tom"))
builder.Bcc.Add(New MailBox("john@example.com", "John"))

builder.Subject = "Put subject here"
builder.Htm = "Put <strong>HTML</strong> message here."

' Plain text is automatically generated, but you can change it:
'builder.Text ="Put plain text message here."

Dim email As IMail = builder.Create()

' Send the message
Using smtp As New Smtp()
	smtp.Connect("server.example.com")    ' or ConnectSSL for SSL
	smtp.UseBestLogin("user", "password")  ' remove if not needed

	smtp.SendMessage(email)

	smtp.Close()
End Using

Also take a look at Mail.dll’s templating engine

Encrypted private key, RSA private key in PEM file

PEM stands for Privacy Enhanced Mail format.

PemReader pem = new PemReader();
RSACryptoServiceProvider rsa = pem.ReadEncryptedPrivateKeyFromFile(
   "EncryptedPrivateKey.pem", // "EncryptedRSAPrivateKey.pem"
   "cypher");

This code handles following formats:

PKCS #8 EncryptedPrivateKeyInfo Encrypted Format:

-----BEGIN ENCRYPTED PRIVATE KEY-----
MIICojAcBgoqhkiG9w0BD .....


Private Key (Traditional SSLeay RSAPrivateKey format) Encrypted:

-----BEGIN RSA PRIVATE KEY-----
Proc-Type: 4,ENCRYPTED
DEK-Info: DES-EDE3-CBC,24A667C253F8A1B9

mKz .....


You can remove the passphrase from the private key:
openssl rsa -in EncryptedPrivateKey.pem -out PrivateKey.pem

Unencrypted private key in PEM file

PemReader pem = new PemReader();
RSACryptoServiceProvider rsa = pem.ReadPrivateKeyFromFile(
   "PrivateKey.pem");

This code handles following formats:

PKCS #8 PrivateKeyInfo Unencrypted:

-----BEGIN PRIVATE KEY-----
MIICdgIBADANBgkqhkiG9w0B ......


Private Key (Traditional SSLeay RSAPrivateKey format) Unencrypted:

-----BEGIN RSA PRIVATE KEY-----
MIICXQIBAAKBgQCcHVm .....


Public key in PEM file

PemReader pem = new PemReader();
RSACryptoServiceProvider rsa = pem.ReadPublicKeyFromFile(
   "PublicKey.pem")

This code handles following formats:

Public Key (SubjecPublicKeyInfo):

-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEB .....


Certificate/private key in PFX file

X509Certificate2 certificate  = new X509Certificate2(
   "certificate.pfx",
   "",
   X509KeyStorageFlags.PersistKeySet)

if (certificate.HasPrivateKey)
{
  using (RSACryptoServiceProvider rsa = (RSACryptoServiceProvider)certificate.PrivateKey)
  {
  }
}

Certificate in PEM/CER file

Note: The private key is never stored in a .pem/.cer file.

X509Certificate2 certificate = new X509Certificate2(
   "certificate.cer");

-or-

PemReader pem = new PemReader();
X509Certificate2 certificate = pem.ReadCertificateFromFile(
   "certificate.cer");

This code handles following formats:


-----BEGIN CERTIFICATE-----
MIIFsTCCA5mgAwIBAgIKYQ .....


Mail.dll .NET email component includes high accuracy anti-spam filter.

It uses enhanced naive Bayesian classifier, specifically modified to handle email messages. Bayesian spam filters are a very powerful technique for dealing with spam.

In our tests we achieved 99,6% accuracy with very low false positive spam detection rates (9 false positives in 54’972 emails tested – that’s 0.016%).

Training

First in the learning phase, you need to teach the classifier to recognize spam and non-spam (ham) messages. You need to prepare 100-200 spam and ham messages.

I suggest using following folder structure:

“Learn” folder is used for training the filter. Both spam and ham folders should contain around 100-200 messages each (the more the better). The number of messages in spam and ham folders must be equal. You can find a spam archive on the bottom of the article.

Messages must be in eml format with correct line endings (rn or 13 10 hex).

Now we use SpamFilterTeacher class to teach BayesianMailFilter:

// C#
using Limilabs.Mail.Tools.Spam;

BayesianMailFilter filter = new BayesianMailFilter();
SpamFilterTeacher teacher = new SpamFilterTeacher(filter);
teacher.TeachSpam(@"c:\bayes\learn\spam");
teacher.TeachHam(@"c:\bayes\learn\ham");

Testing

“Test” folder is used for testing our filter:

// C#

SpamTestResults r = teacher.Test(
    @"c:\bayes\test\spam",
    @"c:\bayes\test\ham");

Console.WriteLine(r);
r.FalsePositives.ForEach(Console.WriteLine);
r.NotMarkedAsSpam.ForEach(Console.WriteLine);

The results should be similar to this:

Accuracy=0.9949, False positives=9, Not marked as spam=271, Tests count=54972
c:\bayes\test\ham/16874.eml
...


When the filter is trained and the results are satisfactory, you can save it to disk:

// C#

filter.Save("c:\20111022.mbayes");

Using

You can load the filter from disk and check individual messages:

// C#

BayesianMailFilter filter = new BayesianMailFilter();
filter.Load("c:\20111022.mbayes");

// you can use Mail.dll to download mesage from POP3 or IMAP server:
string eml = ...

IMail email = new MailBuilder().CreateFromEml(eml);

SpamResult result = filter.Examine(email);
Console.WriteLine(result.Probability);
Console.WriteLine(result.IsSpam);

If the filter incorrectly recognizes the message you can train it again:

// C#

filter.LearnSpam(email);
// - or -
filter.LearnHam(email);

filter.Save("c:\20111022.mbayes");

Spam archives

For most recent spam you can check this great archive: http://www.untroubled.org/spam/.
Unfortunately messages don’t have correct extension (*.eml) and line endings are incorrect.

You can download spam archive including 7874 spam messages from Oct 2011 here:
http://www.limilabs.com/static/mail/spam/spam201110.zip