I'm not quite sure, but I believe that the MIME Types are configured in the <tt><INSTALL-FOLDER>/conf/web.xml</tt>. However, I'm sure that S/MIME is an unsupported type (see the link below):
Also, perhaps the following link related to JIRA encoding could be useful to understand a little bit about it.
For further details, perhaps you should raise a new support ticket in SAC.
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