Disable folder notify setting on Android 7 Nougat and before

Notification grouping is available on Android 7 Nougat and later only
Showing a notification per message is not a good idea
The summary notification is used to navigate to the unified inbox

FAQ.md

@@ -407,7 +407,10 @@ See [this FAQ](#user-content-faq21) if your device has a notification light.
 <a name="faq29"></a>
 **(29) How can I get new message notifications for other folders?**
 
-Just long press the folder, select *Edit properties*, enable *Notify new messages* and tap *Save*.
+Just long press a folder, select *Edit properties*,
+and enable either *Show in unified inbox*
+or *Notify new messages* (available on Android 7 Nougat and later only)
+and tap *Save*.
 
 <a name="faq30"></a>
 **(30) How can I use the provided quick settings?**

README.md

@@ -37,7 +37,7 @@ See also [this FAQ](https://github.com/M66B/open-source-email/blob/master/FAQ.md
 * Dark/black theme
 * Account/identity colors
 * Notifications per account
-* Notifications with message preview
+* Notifications with message preview (requires Android 7 Nougat or later)
 * Reply templates
 * Search on server
 * Keyword management
@@ -85,6 +85,8 @@ Certificate fingerprints:
 ## Compatibility
 
 FairEmail requires at least Android 5 Lollipop.
+Individual message notifications are available on Android 7 Nougat and later only
+because earlier Android versions do not support notification grouping.
 
 FairEmail will work properly on devices without any Google service installed.
 

app/src/main/java/eu/faircode/email/FragmentFolder.java

@@ -21,6 +21,7 @@ package eu.faircode.email;
 
 import android.content.Context;
 import android.content.DialogInterface;
+import android.os.Build;
 import android.os.Bundle;
 import android.text.TextUtils;
 import android.util.Log;
@@ -109,6 +110,9 @@ public class FragmentFolder extends FragmentEx {
             }
         });
 
+        // Navigating to individual messages requires notification grouping
+        cbNotify.setVisibility(Build.VERSION.SDK_INT >= Build.VERSION_CODES.N ? View.VISIBLE : View.GONE);
+
         btnSave.setOnClickListener(new View.OnClickListener() {
             @Override
             public void onClick(View v) {
@@ -125,7 +129,7 @@ public class FragmentFolder extends FragmentEx {
                 args.putBoolean("unified", cbUnified.isChecked());
                 args.putBoolean("synchronize", cbSynchronize.isChecked());
                 args.putBoolean("poll", cbPoll.isChecked());
-                args.putBoolean("notify", cbNotify.isChecked());
+                args.putBoolean("notify", cbNotify.getVisibility() == View.VISIBLE && cbNotify.isChecked());
                 args.putString("sync", etSyncDays.getText().toString());
                 args.putString("keep", etKeepDays.getText().toString());