DKIM.Net

DomainKeys Identified Mail (DKIM) and Domain Key email signing for .Net Framework

Known Issues

As System.Net.Mail.SmtpClient generates boundary identifiers randomly and as this code hacks the SmtpClient to retrieve the full email content before sending the code cannot be used when sending with SmtpClient and the MailMessage when the MailMessage has an alternative view or an attachment.

Example - Sending with SmtpClient

    var msg = new MailMessage();

    msg.From = new MailAddress("me@mydomain.com", "Joe Bloggs");
    msg.To.Add(new MailAddress("check-auth@verifier.port25.com", "Port25"));
    msg.Subject = "Testing DKIM.Net";
    msg.Body = "Hello World";

    var privateKey = PrivateKeySigner.Create(@"-----BEGIN RSA PRIVATE KEY-----
    ....
    -----END RSA PRIVATE KEY-----");

    var domainKeySigner = new DomainKeySigner(privateKey, "mydomain.com", "abc", new string[] { "From", "To", "Subject" });
    msg.DomainKeySign(domainKeySigner);

    var dkimSigner = new DkimSigner(privateKey, "mydomain.com", "abc", new string[] { "From", "To", "Subject" });
    msg.DkimSign(dkimSigner);

    new SmtpClient().Send(msg);

Example - DNS Records

Domain Key settings

_domainkey "o=~;r=admin@mydomain.com"

Domain Key / DKIM selector

selector._domainkey "k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDetWmczoNly/wfDc5WH8F2o42kGjYG7bbmfxjNP2y2qZja84v5W8z8SL702w3N5ZwQLdQmuQ8yN4WOYrg8DHGOB6g+xVP3h1Hr1+C05Vk/x3BXw0wIffNqcVzPkRNNNILtiwPJhhlDVMvaTx20vrrCAz9i6CX6Onj4OWxUaAjtuQIDAQAB"