SSL Email And SMTP Error - WHM/cPanel - Retail Host Certificate

We have a few users that use SSL email and we decided to purchase a cheap single-root SSL cert over at namecheap for the host name so that it would end the "self-signed cert" whining.

We got the cert installed and it works great for WHM/cPanel and also works for SSL over IMAP and POP3, but the very first email anyone sends (SMTP) per day gives this warning (Outlook Express):

The server you are connected to is using a security certificate that could not be verified.
A certificate chain processed, but terminated in a root certificate which is not trusted by the trust provider.

It seems obvious that the cert used by the SMTP system is not the new one we installed.

We used WHM's SSL/TLS -> Change Server Certificates link to install the cert.

We then made sure that:

/usr/share/ssl/certs/host.domain.com.crt
/usr/share/ssl/private/host.domain.com.key
/etc/exim.crt
/etc/exim.key

...all contained the current cert or key as appropriate.

Just for grins, we even made sure:
/usr/local/cpanel/etc/cpanel.pem
...had the correct pair.

We restarted all the mail services and even restarted the whole server. (I know...Windows reaction...bad tech.)

Does anyone know of a stealth location where the SSL cert for SMTP should be updated?

WHM 10.8.0 cPanel 10.9.0-R139
CentOS 3.8 i686 - WHM X v3.1.0