When you upgrade your server to 8.51 the mail85.ntf template is improved slightly, but it it still called Mail85.ntf and it is not obvious.

How do you know if you are using the mail 8.51 template?

If you open up the template or a mail file based upon the template and right click on the Trash Icon it will say "Empty Trash" if you are in 8.51 .

Also you can accept meeting invites from the preview pane, but you probably have not got an invite in your template.