In previous section, I introduced how to parse email. In this section, I will introduce how to verify digital signature and decrypt email in VB 6.0.
How to sign email?
Digital signature is always signed by sender certificate. The certificate used to sign email content MUST have the public/private key pair.
First of all, the user MUST get a digital certificate for personal email protection from third-party certificate authorities such as www.verisign.com.
After the certificate is installed on the machine, it can be viewed by
Internet Options ->
When you view the certificate, please note there is a line “You have a private key that corresponds
to this certificate” in the certificate view, that means you are able to
use this certificate to sign email content. If this line doesn’t appear, that means
you are unable to sign the email content by this certificate.
To sign email content, please refer to EASendMail SMTP Component.
How to encrypt email?
Encrypting email doesn’t require sender certificate but the certificate with public key for every recipient.
firstname.lastname@example.org sends an email to
with digital signature; The digital signature contains the public key certificate for
email@example.com can send an encrypted email with this certificate back to
from@adminsystem can read this email, because this email MUST be decrypted by private key of
Therefore, you MUST receive an digital signed email from other people (Most email clients such as outlook, outlook express will add the certificate to the Other People Storage automatically once an digital signed email is received) before you can send encrypted email to this people.
To encrypt email, please refer to EASendMail SMTP Component.
Remarks: All of examples in this section are based on first section: A simple VB 6.0 project. To compile and run the following example codes successfully, please click here to learn how to create the test project and add reference to your project.
The following example codes demonstrate how to use EAGetMail POP3 component to verify digital signature and decrypt email.
To get the full sample projects, please refer to Samples section.
Option Explicit Const CRYPT_MACHINE_KEYSET = 32 Const CRYPT_USER_KEYSET = 4096 Const CERT_SYSTEM_STORE_CURRENT_USER = 65536 Const CERT_SYSTEM_STORE_LOCAL_MACHINE = 131072 Private Sub ParseEmail(ByVal emlFile As String) Dim oMail As New EAGetMailObjLib.Mail oMail.LicenseCode = "TryIt" On Error GoTo ErrorHandle oMail.LoadFile emlFile, False If oMail.IsEncrypted Then ' This email is encrypted, we decrypt it by user default certificate. ' You can also use specified certificate like this ' Dim oCert As New EAGetMailObjLib.Certificate ' oCert.LoadFromFile "c:\test.pfx", "pfxpassword", CRYPT_USER_KEYSET ' Set oMail = oMail.Decrypt(oCert) Set oMail = oMail.Decrypt(Nothing) End If If oMail.IsSigned Then ' This email is digital signed. Dim oCert As EAGetMailObjLib.Certificate Set oCert = oMail.VerifySignature MsgBox "This email contains a valid digital signature." ' You can add the certificate to your certificate storage like this ' oCert.AddToStore CERT_SYSTEM_STORE_CURRENT_USER, "addressbook" ' Then you can use send the encrypted email back to this sender. End If ' Parse email sender MsgBox "From: " & oMail.From.Address Dim arAddr Dim i As Integer Dim addr As EAGetMailObjLib.MailAddress ' Parse email to recipients arAddr = oMail.To For i = LBound(arAddr) To UBound(arAddr) Set addr = arAddr(i) MsgBox "To: " & addr.Address Next ' Parse email cc arAddr = oMail.Cc For i = LBound(arAddr) To UBound(arAddr) Set addr = arAddr(i) MsgBox "Cc: " & addr.Address Next ' Parse email subject MsgBox "Subject: " & oMail.Subject ' Parse email text body MsgBox "Text body: " & oMail.TextBody ' Parse email HTML body MsgBox "Html body: " & oMail.HtmlBody Dim atts Dim att As EAGetMailObjLib.Attachment ' Parse attachments atts = oMail.Attachments For i = LBound(atts) To UBound(atts) Set att = atts(i) MsgBox "Attachment: " & att.name Next Exit Sub ErrorHandle: MsgBox Err.Description End Sub Private Sub Command1_Click() Dim curpath As String Dim mailbox As String Dim oTools As New EAGetMailObjLib.Tools ' Create a folder named "inbox" under current directory ' to save the email retrieved. curpath = App.Path mailbox = curpath & "\inbox" oTools.CreateFolder mailbox Dim files Dim i As Long ' Get all *.eml files in specified folder and parse it one by one. files = oTools.GetFiles(mailbox & "\*.eml") For i = LBound(files) To UBound(files) ParseEmail files(i) Next Exit Sub ErrorHandle: MsgBox Err.Description End Sub
At next section I will introduce how to parse MAPI winmail.dat (TNEF/MAPI) attachment.
If you have any comments or questions about above example codes, please click here to add your comments.