All providers of virtuals are (and will always be) required to provide a consistent interface jar. In the case of javamail it will be a mail.jar for example jarfrom --virtual <virtual> <interface.jar> !rdep gnu-javamail [22:55] <jeeves> dev-java/gnu-javamail <- dev-java/mx4j-tools dev-java/mx4j:examples
Done ages ago.