PowerShell

Verify DKIM-Signature Headers in Downloaded Email

See more DKIM / DomainKey Examples

Downloads email from an IMAP server and verifies the DKIM-Signature header(s) in each email, if present. PowerShell

Add-Type -Path "C:\chilkat\ChilkatDotNet47-x64\ChilkatDotNet47.dll"

$success = $false

# This example requires the Chilkat API to have been previously unlocked.
# See Global Unlock Sample for sample code.

$imap = New-Object Chilkat.Imap

# Connect to an IMAP server, login, select mailbox..
# Use TLS 
$imap.Ssl = $true
$imap.Port = 993
$success = $imap.Connect("imap.example.com")
if ($success -eq $true) {
    $success = $imap.Login("myLogin","myPassword")
    if ($success -eq $true) {
        $success = $imap.SelectMailbox("Inbox")
    }

}

if ($success -ne $true) {
    $($imap.LastErrorText)
    exit
}

$dkim = New-Object Chilkat.Dkim

# Download a max of 10 emails and verify any DKIM-Signature headers
# that are present.

# Download emails by sequence numbers (not UIDs).
$bUid = $false

$n = $imap.NumMessages
if ($n -gt 10) {
    $n = 10
}

$json = New-Object Chilkat.JsonObject
$json.EmitCompact = $false

# To verify DKIM-Signature headers, we need the exact unmodified MIME bytes of each email.
$mimeData = New-Object Chilkat.BinData
$seqNum = 1
while ($seqNum -le $n) {
    # The FetchSingleBd method was introduced in v9.5.0.76
    $success = $imap.FetchSingleBd($seqNum,$bUid,$mimeData)
    if ($success -ne $true) {
        $($imap.LastErrorText)
        exit
    }

    # Get the number of DKIM-Signature headers.
    $numDkim = $dkim.NumDkimSigs($mimeData)

    # Verify each..
    $j = 0
    while ($j -lt $numDkim) {
        $("------ DKIM Signature " + $j)

        $success = $dkim.DkimVerify($j,$mimeData)
        if ($success -ne $true) {
            $("Not valid.")
        }
        else {
            $("valid.")
        }

        # Show the additional information about the signature verification
        $json.Load($dkim.VerifyInfo)
        $($json.Emit())

        # The JSON contains information such as this:

        # 	{
        # 	  "domain": "amazonses.com",
        # 	  "selector": "7v7vs6w47njt4pimodk5mmttbegzsi6n",
        # 	  "publicKey": "MIGfMA0GCSqG...v2GvWPqGHz6uqeQIDAQAB",
        # 	  "canonicalization": "relaxed/simple",
        # 	  "algorithm": "rsa-sha256",
        # 	  "signedHeaders": "Subject:From:To:Date:Mime-Version:Content-Type:References:Message-Id:Feedback-ID",
        # 	  "verified": "yes"
        # 	}

        $j = $j + 1
    }

    $seqNum = $seqNum + 1
}

$success = $imap.Disconnect()