Apache Mime4j is developed by the Apache James team but now
has a dedicated mailing list.
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. It 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. However, mime4j does include
facilities to decode bodies and fields and the Message class
described below handles decoding of fields and bodies