/// <summary>
/// Signs the given mail item, if possible, according to the DKIM standard.
/// </summary>
/// <param name="mailItem">The mail item that is to be signed, if possible.</param>
private void SignMailItem(MailItem mailItem)
{
// If the mail item is a "system message" then it will be read-only here,
// and we can't sign it. Additionally, if the message has a "TnefPart",
// then it is in a proprietary format used by Outlook and Exchange Server,
// which means we shouldn't bother signing it.
if (!mailItem.Message.IsSystemMessage && mailItem.Message.TnefPart == null)
{
string domainPart = null;
/* Check if we have a valid From address */
if (!mailItem.FromAddress.IsValid || mailItem.FromAddress.DomainPart == null)
{
// The FromAddress is empty. Try to get the domain from somewhere else (see https://github.com/Pro/dkim-exchange/issues/99)
string smtpAddress = (mailItem.Message != null && mailItem.Message.Sender != null) ? mailItem.Message.Sender.SmtpAddress : null;
if (smtpAddress != null && smtpAddress.Length > 0)
{
try
{
domainPart = new MailAddress(smtpAddress).Host;
}
catch (FormatException)
{
// do nothing
}
}
if (domainPart == null)
{
Logger.LogWarning("Invalid from address '" + mailItem.FromAddress + "' and invalid SmtpAddress '" + smtpAddress + "'. Not signing email.");
return;
}
}
else
{
// from address is valid
domainPart = mailItem.FromAddress.DomainPart;
}
/* If domain was found in define domain configuration */
if (dkimSigner.GetDomains().ContainsKey(domainPart))
{
try
{
dkimSigner.SignMessage(dkimSigner.GetDomains()[domainPart], mailItem);
}
catch (Exception ex)
{
Logger.LogError("Could not sign message: " + ex.Message);
}
}
else
{
Logger.LogDebug("No entry found in config for domain '" + domainPart + "'");
}
}
else
{
Logger.LogDebug("Message is a System message or of TNEF format. Not signing.");
}
}
