I'm using MimeKit to send emails and the use of DKIM to sign them has been broached. I've looked at the example on the MimKit site, and googled the terms but found no answers.
Public Shared Sub DkimSign(ByVal message As MimeMessage)
Dim headers = New HeaderId() {HeaderId.From, HeaderId.Subject, HeaderId.Date}
Dim headerAlgorithm = DkimCanonicalizationAlgorithm.Simple
Dim bodyAlgorithm = DkimCanonicalizationAlgorithm.Simple
Dim signer = New DkimSigner("filename", "domain", "selector") With {.SignatureAlgorithm = DkimSignatureAlgorithm.RsaSha1, .AgentOrUserIdentifier = "@eng.example.com"}
message.Prepare(EncodingConstraint.SevenBit)
message.Sign(signer, headers, headerAlgorithm, bodyAlgorithm)
End Sub
When instantiating the signer it requires a filename, domain and selector. If I'm sending an email from "bob@website.com" I would assume that the physical file would be placed on the root of the site and the instantiation would look something like this:
Dim signer = New DkimSigner("dkim.txt", "website.com", "") With {.SignatureAlgorithm = DkimSignatureAlgorithm.RsaSha1, .AgentOrUserIdentifier = "???"}
But not sure the format/reason for the AgentOrUserIdentifier ... can anyone edify me or correct me if my assumptions are wrong?
The fileName parameter is the path to the private key that should be used for signing the message. I'm not sure why you expect it to be at the root of the site or why it would be called dkim.txt, but I can almost guarantee that both assumptions are wrong.
A selector is used by the receiving client to locate the correct public key in the DNS records because it's possible for the same domain to have multiple keys that it uses for signing.
The AgentOrUserIdentifier corresponds to the i= parameter that you find in the DKIM-Signature header and specifies the user or agent that is taking responsibility for the signature.