Hijacking this issue as placeholder for security upgrade.
original text:
The smime-module has dependency on utils-mail-smime and it has dependency on bcjmail-jdk15to18 along with further transitive dependencies from Bouncy Castle.
From your this comment @bbottema I come to know that you are in process of updating 3rd party dependencies, hence consider a suggestion of using bcjmail-jdk18on instead of bcjmail-jdk15to18 as simple-java-mail is compatible from JDK8+.
Also, bc-jdk15to18 JARs are designed to be compatible with JDK versions 1.5 through 1.8, where on other hand bc-jdk18on are designed to be compatible with JDK 1.8 and later versions. So it makes sense, isn't it? even the https://bouncycastle.org/latest_releases.html also says the same.
Please ignore if you have already considered this :)
Hijacking this issue as placeholder for security upgrade.
original text: