mime4j provides a parser, MimeStreamParser, for e-mail message streams in plain RFC822 and MIME format. The parser uses a callback mechanism to report parsing events such as the start of an entity header, the start of a body, etc. If you are familiar with the SAX XML parser interface you should have no problem getting started with mime4j. The parser only deals with the structure of the message stream and won't do any decoding of base64 or quoted-printable encoded header fields and bodies. This is intentional - the parser should only provide the most basic functionality needed to build more complex parsers.
URL: James mime4j - Mime4j