Updated FAQ

FAQ.md

@@ -627,7 +627,7 @@ This can be caused by using an incorrect host name, so first double-check the ho
 Please see the documentation of the email provider about the right host name.
 Sometimes the right host name is in the error message.
 
-Another possible cause is [Certificate transparency](https://github.com/appmattus/certificatetransparency) failing, so try disabling it in the connection settings tab page.
+~~Another possible cause is [Certificate transparency](https://github.com/appmattus/certificatetransparency) failing, so try disabling it in the connection settings tab page.~~
 
 You should try to fix this by contacting your provider or by getting a valid security certificate
 because invalid security certificates are insecure and allow [man-in-the-middle attacks](https://en.wikipedia.org/wiki/Man-in-the-middle_attack).
@@ -648,6 +648,7 @@ This will "pin" the server certificate to prevent man-in-the-middle attacks.
 
 Note that older Android versions might not recognize newer certification authorities like Let’s Encrypt causing connections to be considered insecure,
 see also [here](https://developer.android.com/training/articles/security-ssl).
+In such cases, you can install the required root/intermediate certificates, for example, the often used [Let's encrypt root certificates](https://letsencrypt.org/ca/certificates/).
 
 <br />
 

index.html

@@ -562,7 +562,7 @@ Therefore, this issue can only be resolved by your email provider,
 or by installing the GitHub version of the app (as an update) and enabling insecure connections in the account/identity settings.** -->
 <p><em>… Untrusted … not in certificate …</em><br /> <em>… Untrusted … Unacceptable certificate …</em><br /> <em>… Invalid security certificate (Can’t verify identity of server) …</em><br /> <em>… Chain validation failed … timestamp check failed … Certificate expired at …</em><br /></p>
 <p>This can be caused by using an incorrect host name, so first double-check the host name in the advanced identity/account settings (tap <em>Manual setup and account options</em>). Please see the documentation of the email provider about the right host name. Sometimes the right host name is in the error message.</p>
-<p>Another possible cause is <a href="https://github.com/appmattus/certificatetransparency">Certificate transparency</a> failing, so try disabling it in the connection settings tab page.</p>
+<p><del>Another possible cause is <a href="https://github.com/appmattus/certificatetransparency">Certificate transparency</a> failing, so try disabling it in the connection settings tab page.</del></p>
 <p>You should try to fix this by contacting your provider or by getting a valid security certificate because invalid security certificates are insecure and allow <a href="https://en.wikipedia.org/wiki/Man-in-the-middle_attack">man-in-the-middle attacks</a>. If money is an obstacle, you can get free security certificates from <a href="https://letsencrypt.org">Let’s Encrypt</a>.</p>
 <p>The quick, but unsafe solution (not advised), is to enable <em>Insecure connections</em> in the advanced identity settings (navigation menu, tap <em>Settings</em>, tap <em>Manual setup</em>, tap <em>Identities</em>, tap the identity, tap <em>Advanced</em>).</p>
 <p>Alternatively, you can accept the fingerprint of invalid server certificates like this:</p>
@@ -574,7 +574,7 @@ or by installing the GitHub version of the app (as an update) and enabling insec
 <li>Tick the checkbox below the error message and save again</li>
 </ol>
 <p>This will “pin” the server certificate to prevent man-in-the-middle attacks.</p>
-<p>Note that older Android versions might not recognize newer certification authorities like Let’s Encrypt causing connections to be considered insecure, see also <a href="https://developer.android.com/training/articles/security-ssl">here</a>.</p>
+<p>Note that older Android versions might not recognize newer certification authorities like Let’s Encrypt causing connections to be considered insecure, see also <a href="https://developer.android.com/training/articles/security-ssl">here</a>. In such cases, you can install the required root/intermediate certificates, for example, the often used <a href="https://letsencrypt.org/ca/certificates/">Let’s encrypt root certificates</a>.</p>
 <p><br /></p>
 <p><em>Trust anchor for certification path not found</em></p>
 <p><em>… java.security.cert.CertPathValidatorException: Trust anchor for certification path not found …</em> means that the default Android trust manager was not able to verify the server certificate chain.</p>