Major plugin refactor and cleanup.

Switched to POCO library for unified platform/library interface.
Deprecated the external module API. It was creating more problems than solving.
Removed most built-in libraries in favor of system libraries for easier maintenance.
Cleaned and secured code with help from static analyzers.

vendor/POCO/NetSSL_OpenSSL/include/Poco/Net/SecureSMTPClientSession.h

@@ -0,0 +1,93 @@
+//
+// SecureSMTPClientSession.h
+//
+// Library: NetSSL_OpenSSL
+// Package: Mail
+// Module:  SecureSMTPClientSession
+//
+// Definition of the SecureSMTPClientSession class.
+//
+// Copyright (c) 2010, Applied Informatics Software Engineering GmbH.
+// and Contributors.
+//
+// SPDX-License-Identifier:	BSL-1.0
+//
+
+
+#ifndef Net_SecureSMTPClientSession_INCLUDED
+#define Net_SecureSMTPClientSession_INCLUDED
+
+
+#include "Poco/Net/NetSSL.h"
+#include "Poco/Net/SMTPClientSession.h"
+#include "Poco/Net/Context.h"
+
+
+namespace Poco {
+namespace Net {
+
+
+class NetSSL_API SecureSMTPClientSession: public SMTPClientSession
+	/// This class implements an Simple Mail
+	/// Transfer Protocol (SMTP, RFC 2821)
+	/// client for sending e-mail messages that
+	/// supports the STARTTLS command for secure
+	/// connections.
+	///
+	/// Usage is as follows:
+	///   1. Create a SecureSMTPClientSession object.
+	///   2. Call login() or login(hostname).
+	///   3. Call startTLS() to switch to a secure connection.
+	///      Check the return value to see if a secure connection
+	///      has actually been established (not all servers may
+	///      support STARTTLS).
+	///   4. Call any of the login() methods to securely authenticate
+	///      with a username and password.
+	///   5. Send the message(s).
+{
+public:
+	explicit SecureSMTPClientSession(const StreamSocket& socket);
+		/// Creates the SecureSMTPClientSession using
+		/// the given socket, which must be connected
+		/// to a SMTP server.
+
+	SecureSMTPClientSession(const std::string& host, Poco::UInt16 port = SMTP_PORT);
+		/// Creates the SecureSMTPClientSession using a socket connected
+		/// to the given host and port.
+
+	virtual ~SecureSMTPClientSession();
+		/// Destroys the SMTPClientSession.
+
+	bool startTLS();
+		/// Sends a STARTTLS command and, if successful,
+		/// creates a secure SSL/TLS connection over the
+		/// existing socket connection.
+		///
+		/// Must be called after login() or login(hostname).
+		/// If successful, login() can be called again
+		/// to authenticate the user.
+		///
+		/// Returns true if the STARTTLS command was successful,
+		/// false otherwise.
+
+	bool startTLS(Context::Ptr pContext);
+		/// Sends a STARTTLS command and, if successful,
+		/// creates a secure SSL/TLS connection over the
+		/// existing socket connection.
+		///
+		/// Uses the given Context object for creating
+		/// the SSL/TLS connection.
+		///
+		/// Must be called after login() or login(hostname).
+		/// If successful, login() can be called again
+		/// to authenticate the user.
+		///
+		/// Returns true if the STARTTLS command was successful,
+		/// false otherwise.
+};
+
+
+} } // namespace Poco::Net
+
+
+#endif // Net_SecureSMTPClientSession_INCLUDED