I installed a Certificate of Let’s Encrypt because of くりくりさん’s comments and it was successful. But I’ve not understood very well, yet. How can I renew the certificate? What procedures do I need to have SAN support certificate? I found ‘HOW TO’ for Exchange 2016, but mine is Apache.
I should study more about Let’s Encrypt.
I posted the article “How to install a Let’s Encrypt Certificate supports SAN to Apache on Windows”.