Define criteria on all pages (#1980)

docs/email-clients.en.md

@@ -205,3 +205,27 @@ Canary Mail is closed-source. We recommend it due to the few choices there are f
 
         - [:simple-apple: macOS](https://neomutt.org/distro)
         - [:simple-linux: Linux](https://neomutt.org/distro)
+
+## Criteria
+
+**Please note we are not affiliated with any of the projects we recommend.** In addition to [our standard criteria](about/criteria.md), we have developed a clear set of requirements to allow us to provide objective recommendations. We suggest you familiarize yourself with this list before choosing to use a project, and conduct your own research to ensure it's the right choice for you.
+
+!!! example "This section is new"
+
+    We are working on establishing defined criteria for every section of our site, and this may be subject to change. If you have any questions about our criteria, please [ask on our forum](https://discuss.privacyguides.net/latest) and don't assume we didn't consider something when making our recommendations if it is not listed here. There are many factors considered and discussed when we recommend a project, and documenting every single one is a work-in-progress.
+
+### Minimum Qualifications
+
+- Apps developed for open-source operating systems must be open-source.
+- Must not collect telemetry, or have an easy way to disable all telemetry.
+- Must support OpenPGP message encryption.
+
+### Best-Case
+
+Our best-case criteria represents what we would like to see from the perfect project in this category. Our recommendations may not include any or all of this functionality, but those which do may rank higher than others on this page.
+
+- Should be open-source.
+- Should be cross-platform.
+- Should not collect any telemetry by default.
+- Should support OpenPGP natively, i.e. without extensions.
+- Should support storing OpenPGP encrypted emails locally.