[Exim] Upgrading from 3.35 to 4.30 q: SMTP Auth

I have a question about upgrading from 3.35 to 4.30. Currently the 3.35 is in production, but it was not compiled to support SMTP Auth. We are recompiling 4.30 and building SMTP Auth support in the Local/Makefile. Do we need to do anything special to run 4.30 from 3.35? In the EDITME file, after setting SMTP Auth support on, I read that we will need a certificate and tell Exim how to find the certificate. I'm not familiar with obtaining a certificate. Could someone please explain?

Thanks so much.

Gene Brotherton