Add Message-ID header in email when not set. (#2915)

Google Mail and others started requesting Message-ID header to be present, otherwise messages are blocked/getting marked as spam.

Sming/Components/Network/src/Network/SmtpClient.cpp

@@ -21,6 +21,7 @@
 #include <Data/Stream/QuotedPrintableOutputStream.h>
 #include <Data/Stream/Base64OutputStream.h>
 #include <Data/HexString.h>
+#include <Data/Uuid.h>
 #include <Crypto/Md5.h>
 #include <Network/Ssl/Factory.h>
 
@@ -296,6 +297,12 @@ void SmtpClient::sendMailHeaders(MailMessage* mail)
 		mail->stream = std::make_unique<QuotedPrintableOutputStream>(mail->stream.release());
 	}
 
+	if(!mail->headers.contains(F("Message-ID"))) {
+		Uuid uuid;
+		uuid.generate();
+		mail->headers[F("Message-ID")] = "<" + uuid.toString() + "@" + url.Host + ">";
+	}
+
 	if(!mail->attachments.isEmpty()) {
 		MultipartStream* mStream = new MultipartStream(MultipartStream::Producer(&SmtpClient::multipartProducer, this));
 		MultipartStream::BodyPart text;