Add Each Part
Use the insertPart() function of RWMimeMultipart to add each MIME part to the multipart:
 
RWMimePart part1;
 
// ... fill part1 with content.
 
RWMimePart part2;
 
// ... fill part2 with content.
 
RWMimeMultipart multipartMessage;
 
multipartMessage.insertPart(part1);
multipartMessage.insertPart(part2);
Add the parts in the order in which they should appear in the multipart.
NOTE: An RWMimeMultipart must not contain itself, either directly or indirectly. A part that contains itself cannot be represented as a string.