diff --git a/Net/include/Poco/Net/MailMessage.h b/Net/include/Poco/Net/MailMessage.h
index 474186036..0042c3e05 100644
--- a/Net/include/Poco/Net/MailMessage.h
+++ b/Net/include/Poco/Net/MailMessage.h
@@ -22,7 +22,9 @@
 #include "Poco/Net/MessageHeader.h"
 #include "Poco/Net/MailRecipient.h"
 #include "Poco/Net/PartStore.h"
+#include "Poco/SharedPtr.h"
 #include "Poco/Timestamp.h"
+#include <sstream>
 #include <vector>
 
 
@@ -34,6 +36,7 @@ class MediaType;
 class PartSource;
 class PartHandler;
 class MultipartWriter;
+class MultipartSource;
 
 
 class Net_API MailMessage: public MessageHeader
@@ -263,8 +266,8 @@ protected:
 	void makeMultipart();
 	void writeHeader(const MessageHeader& header, std::ostream& ostr) const;
 	void writeMultipart(MessageHeader& header, std::ostream& ostr) const;
-	void writePart(MultipartWriter& writer, const Part& part) const;
-	void writeEncoded(std::istream& istr, std::ostream& ostr, ContentTransferEncoding encoding) const;
+	static void writePart(MultipartWriter& writer, const Part& part);
+	static void writeEncoded(std::istream& istr, std::ostream& ostr, ContentTransferEncoding encoding);
 	void setRecipientHeaders(MessageHeader& headers) const;
 	void readHeader(std::istream& istr);
 	void readMultipart(std::istream& istr, PartHandler& handler);
@@ -284,6 +287,47 @@ private:
 	ContentTransferEncoding _encoding;
 	mutable std::string     _boundary;
 	PartStoreFactory*       _pStoreFactory;
+
+	friend class MultipartSource;
+};
+
+
+class Net_API MultipartSource: public PartSource
+	/// This is a PartSource for constructing complex
+	/// mail messages consisting of multiple nested parts.
+{
+public:
+	explicit MultipartSource(const std::string contentType = "multipart/alternative");
+		/// Creates an empty MultipartSource.
+		///
+		/// At least one part must be added with addPart().
+
+	~MultipartSource();
+		/// Destroys the MultipartSource.
+
+	void addPart(const std::string& name,
+		PartSource* pSource,
+		MailMessage::ContentDisposition disposition,
+		MailMessage::ContentTransferEncoding encoding);
+		/// Adds a part/attachment to the MultipartSource.
+		///
+		/// The MultipartSource takes ownership of the PartSource and deletes it
+		/// when it is no longer needed.
+		///
+		/// The part name, and the filename specified in the part source
+		/// must not contain any non-ASCII characters.
+		/// To include non-ASCII characters in the part name or filename,
+		/// use RFC 2047 word encoding (see encodeWord()).
+
+	// PartSource
+	std::istream& stream();
+
+protected:
+	static std::string contentTypeWithBoundary(const std::string& contentType);
+
+private:
+	std::vector<MailMessage::Part> _parts;
+	std::stringstream _content;
 };
 
 
diff --git a/Net/src/MailMessage.cpp b/Net/src/MailMessage.cpp
index 3fab8fa46..15347ecd2 100644
--- a/Net/src/MailMessage.cpp
+++ b/Net/src/MailMessage.cpp
@@ -418,7 +418,7 @@ void MailMessage::writeMultipart(MessageHeader& header, std::ostream& ostr) cons
 }
 
 
-void MailMessage::writePart(MultipartWriter& writer, const Part& part) const
+void MailMessage::writePart(MultipartWriter& writer, const Part& part)
 {
 	MessageHeader partHeader(part.pSource->headers());
 	MediaType mediaType(part.pSource->mediaType());
@@ -444,7 +444,7 @@ void MailMessage::writePart(MultipartWriter& writer, const Part& part) const
 }
 
 
-void MailMessage::writeEncoded(std::istream& istr, std::ostream& ostr, ContentTransferEncoding encoding) const
+void MailMessage::writeEncoded(std::istream& istr, std::ostream& ostr, ContentTransferEncoding encoding)
 {
 	switch (encoding)
 	{
@@ -692,4 +692,57 @@ PartSource* MailMessage::createPartStore(const std::string& content, const std::
 }
 
 
+MultipartSource::MultipartSource(const std::string contentType):
+	PartSource(contentTypeWithBoundary(contentType))
+{
+}
+
+
+MultipartSource::~MultipartSource()
+{
+	for (MailMessage::PartVec::iterator it = _parts.begin(); it != _parts.end(); ++it)
+	{
+		delete it->pSource;
+	}
+}
+
+
+void MultipartSource::addPart(const std::string& name,
+	PartSource* pSource,
+	MailMessage::ContentDisposition disposition,
+	MailMessage::ContentTransferEncoding encoding)
+{
+	MailMessage::Part part;
+	part.name        = name;
+	part.pSource     = pSource;
+	part.disposition = disposition;
+	part.encoding    = encoding;
+	_parts.push_back(part);
+}
+
+
+std::istream& MultipartSource::stream()
+{
+	MediaType mt(mediaType());
+	std::string boundary = mt.getParameter("boundary");
+
+	MultipartWriter writer(_content, boundary);
+	for (MailMessage::PartVec::const_iterator it = _parts.begin(); it != _parts.end(); ++it)
+	{
+		MailMessage::writePart(writer, *it);
+	}
+	writer.close();
+
+	return _content;
+}
+
+
+std::string MultipartSource::contentTypeWithBoundary(const std::string& contentType)
+{
+	MediaType mediaType(contentType);
+	mediaType.setParameter("boundary", MultipartWriter::createBoundary());
+	return mediaType.toString();
+}
+
+
 } } // namespace Poco::Net