Symantec has certified Java 8 for Symantec Mail Security for Domino 8.1.3. For builds older than SMSDOM 8.1.3, please consult:
How to use Java 8 with SMSDOM 8.1.2
Once you have a working environment, you can now install Java 8 and then install the JCE for Java 8. You can download the JCE as provided below.
Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files 8 Download
Open the notes.ini file and verify the path for SAVJava= line to point to the Java 8 bin folder. If this line does not exist, you can just add it to your notes.ini. Here is an example: SAVJava=C:\Program Files\Java\jre8\bin\
Now when you run LiveUpdate it will use this path and run using Java 8.
NOTE: If you have SMSDOM installed without LiveUpdate you will then need to follow the steps at one of the following technotes depending on your environment that matches yours and then just substitute installing Java 6 with Java 8 in the steps.
Windows 64bit/Domino 64bit/SMSDOM 64bit - http://www.symantec.com/docs/tech178338
Windows 64bit/Domino 32bit/SMSDOM 32bit - http://www.symantec.com/docs/tech178336
Windows 32bit/Domino 32bit/SMSDOM 32bit - http://www.symantec.com/docs/tech178332