The field "Send all email to this test email address (non-production)" is missing in the email properties page.

All versions.

This is caused because of the fact that the glide.email.test.user property is missing the category in the categories related list.

To fix this :

1) Delete the glide.email.test.user property
2) Export the glide.email.test.user property and the sys_properties_category_m2m entry from a working instance of same version.
3) Import the exported records to the non working instance.