Accoring to the POD for RT::Crypt::SMIME, it is "DEPRECATED": 
This extension is deprecated.  It only works with RT 3.6 which is unsu
+pported.

[download]

Unfortunately, it does not offer an alternative.

In reply to Re: Can't Compile CPAN modules for RT4 by toolic
in thread Cen't Compile CPAN modules for RT4 by bluethundr

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