Here are a few articles we've prepared on technical topics which other people may find helpful.
I had some trouble getting some SSL certificates installed correctly on a new Plesk 8.x hosting server. It took a bunch of research (and emails back and forth with Comodo's support team), but the answer is outlined below. This appears to be platform-independent, so any Plesk 8.x server may be able to benefit from the following information.
When I was installing a new "EssentialSSL" SSL certificate purchased from Comodo on a Plesk 8.x server, everything went okay until I needed to provide the CA Certificate in Plesk. No matter what I tried, when uploading the CA Certificate, Plesk would give a warning stating 'The CA certificate does not sign the certificate'.
Comodo's information (including their own guide for installing under Plesk v7 and v8) tends to indicate that you need to cut and paste an intermediate certificate and a root certificate (in that order, one following the other) into the textbox in the Plesk administration interface (or else uploaded from a file on disk).
When they emailed me the certificate upon purchase, it came with a bundle of THREE certificates (not just the two outlined above). It didn't matter, since whether I obtained the Intermediate and Root certificates from their support website and appended them as instructed, or whether I used the three certificates appended in the provided bundle, neither loaded into Plesk without that warning message.
As it turns out, you actually need FOUR of the CA certificates appended together in a particular order so as to successfully install them into Plesk without warning. This was related to me by Comodo's support staff, and did work successfully when I tested it. This new handmade bundle of CA certificates successfully loaded into Plesk v8.1 without warnings or errors, and successfully secured the new website it had been purchased for.
You should download and append the following CA certificates into a new file, in the following order :
Those files are available for download from Comodo's support area on their website.
The order you place the contents of those files into a new file is important, and should be followed as outlined above. No blank lines should be added between the certificate contents when you copy the contents of the four existing CA certs into a new file. You then provide this new file to Plesk when it asks for the CA Certificate.
Comodo's certificates are otherwise a great value, and I highly recommend their products and services.
The default index page created by Plesk v8.1 for new domains includes a small feed which shows current news headlines gleaned from somewhere else on the web. Since those headlines load on the fly from a non-secure server, the default index page for new domains will not show the tiny lock icon in most web browsers indicating that page is secure. This can be troubling if you are attempting to test whether a newly installed SSL certificate is working properly or not. You should navigate to another page on your newly secured website to verify that your web browser can load pages securely from your domain.