Confirm emerge failure oracle-javamail-1.5.6
Install dev-java/javatoolkit-0.6.5.ebuild and dev-java/oracle-javamail-1.5.6-r1.ebuild from gentoo in your local overlay solves the issue.
In the process of building jedit-5.4.0 and its depends jython-2.7.0-r2 emerge failed.
Emerged jython by going to Bug 758881 - dev-java/jython-2.7.0-r2 AttributeError: 'NoneType' object has no attribute 'startswith' apply jython-2.7.0-r2.ebuild.patch regenerate manifest.
dev-java:jython-2.7.0-r2:20210319-042623.log dev-java:jython-2.7.0-r2:20210319-025110.log
dev-java:oracle-javamail-1.5.6-r1:20210319-185450.log