The quick and easy way would be to simply rename the R7 template name to the R6 template name.
Not to be confusing, I will detail the issue.
A Notes database has three possible names : the filename, the name users see on the workspace, and the template name. Of these three, two are generally filled in : the filename (mandatory) and the db title (generally but not mandatory).
To add to the confusion, filenames can have two possible extensions : nsf and ntf (Notes Storage Format and Notes Template Format). The ntf is generally the extension of template files, but that has nothing to do with the fact that file can be used for updating other files. Actually, the extension doesn't count. What counts is if the file has a template name. Nsf files can very well be used as templates !
The template name is optional and, in fact, most databases do not have a template name. However, many databases inherit their design from a template, which is a database that does have a template name.
The template name is a simple string of characters that should (ideally) uniquely describe the template. For instance, by default all mail files inherit from the Notes Mail template of a given version.
Thus, you should have on your server a template file for R6 mail that is named something like mailR6.ntf. This file (if you check the Properties) has a template name.
If you have upgraded to R7, then you should also have a mailR7.ntf somewhere, with a different template name.
All this explaining now comes to this point : simply copy the R6 template name to the R7 template database. After doing so, do not forget to modify the R6 database template name to something else (add a few chars) to break the link and make the R7 file the "real" template.
That done, the next time the server runs the update task, the design of all mail files that use the R6 template name will be updated to the R7 design.
Now for a word of caution : when upgrading a Notes server, there is generally a procedure that automates updating the mail files. It may not be enough to just update the design, so you should check that there is not a command to enter once the design update is done.
Hope this helps.
Pascal.
I've got nothing to hide, and I'd very much like to keep that away from prying eyes.