The Proposed Changes for JavaMail 1.5 are summarized below, but you can also refer to list of changes on the Project Kenai site.

http://kenai.com/bugzilla/show_bug.cgi?id=5682
add FetchProfile.Item.SIZE
http://kenai.com/bugzilla/show_bug.cgi?id=5683
fix protected fields in final classes in javax.mail.search
http://kenai.com/bugzilla/show_bug.cgi?id=5684
add MimeMultipart(String subtype, BodyPart... bps) constructor
http://kenai.com/bugzilla/show_bug.cgi?id=5685
exceptions should support exception chaining
http://kenai.com/bugzilla/show_bug.cgi?id=5686
ParameterList needs to support use by IMAP
http://kenai.com/bugzilla/show_bug.cgi?id=5687
ContentType.toString & ContentDisposition.toString shouldn't return null
http://kenai.com/bugzilla/show_bug.cgi?id=5689
add Transport.send(msg, username, password) method
http://kenai.com/bugzilla/show_bug.cgi?id=5690
add MimeMessage.setFrom(String) method
http://kenai.com/bugzilla/show_bug.cgi?id=5691
add Message.getSession() method
http://kenai.com/bugzilla/show_bug.cgi?id=5692
MimeBodyPart.attachFile should set the disposition to ATTACHMENT
http://kenai.com/bugzilla/show_bug.cgi?id=5693
add MimeMessage.reply(replyToAll, setAnswered) method
http://kenai.com/bugzilla/show_bug.cgi?id=5694
add "next" methods to HeaderTokenizer to help parsing bad headers
http://kenai.com/bugzilla/show_bug.cgi?id=5743
add @MailSessionDefinition and @MailSessionDefinitions for Java EE 7
http://kenai.com/bugzilla/show_bug.cgi?id=5769
make cachedContent field protected in MimeMessage and MimeBodyPart
http://kenai.com/bugzilla/show_bug.cgi?id=5770
make MimeMultipart fields protected to allow subclassing
http://kenai.com/bugzilla/show_bug.cgi?id=5818
need simple way to override MIME type and encoding of attachment
http://kenai.com/bugzilla/show_bug.cgi?id=5819
enable RFC 2231 support by default