When setting up your SSL in your Plesk package, it is important to make sure you apply the SSL certificate not only to your domain, but your webmail. Use the following instructions to apply the SSL to your email in your Personal/Startup/Business Hosting, or Managed WordPress packages:

Step 1. 

Log in to your Rebel account, then select "Products" in the top-left corner. In the top toolbar, you will see "Hosting. Please select this. 

Step 2. 

Here you will see all of your hosting packages listed. For the one you want to access, select the purple "Control Panel" button. This will lead you to the Plesk interface. 

Step 3.

On the left-hand side menu, please select "Mail".

Step 4.

At the top, please select "Mail Settings".

Step 5.

Here you will be able to directly select the domain name you wish to apply the SSL to.

Step 6.

From the drop-down menu's you will be able to select your SSL/TLS certificate. Once selected please click "OK".