[exim] setting up purchased SSL certificates on existing sys…

This has to be so simple but I can't get my head round it.

I have an existing Cento 7 / Exim server running which I set up some time ago
using self generated certificates.

I have now purchased (through 123-reg) a SSL certificate and I am trying to
install it on the server.

However, copious Google searches all seem to be bringing up the same few
articles, most of which are for specific platforms, e.g. those with cPanel
installed.

Most of these articles discuss a certificate and key pair, and most refer to
the self generation process mentioned above. My exim.conf has the following
lines:

#tls_certificate = /etc/ssl/mail.ringways.co.uk.crt
#tls_privatekey = /etc/ssl/mail.ringways.co.uk.key

tls_certificate = /etc/pki/tls/certs/exim.pem
tls_privatekey = /etc/pki/tls/private/exim.pem

I seem to remember making these changes when I first set up the server using
articles similar to the ones I've just found.

My problem is that from my SSL certificate purchase I have an "Intermediate
Certificate" and a 'SSL Certificate'. The second of which is apparently
formatted for web software including Apache. I did not receive any key files.

Could someone please point me to (easy to understand) instructions on how to
install my new certificate onto Exim (and Dovecot too if possible)


Gary