Removed app DNS cache

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

@@ -465,15 +465,6 @@ public class DnsHelper {
         return result;
     }
 
-    static void clear(Context context) {
-        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
-        SharedPreferences.Editor editor = prefs.edit();
-        for (String key : prefs.getAll().keySet())
-            if (key != null && key.startsWith("dns."))
-                editor.remove(key);
-        editor.apply();
-    }
-
     static boolean hasDnsSec() {
         if (BuildConfig.PLAY_STORE_RELEASE)
             return false;

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

@@ -425,8 +425,6 @@ public class EmailService implements AutoCloseable {
             String certificate, String fingerprint) throws MessagingException {
         properties.put("fairemail.server", host);
 
-        DnsHelper.clear(context);
-
         SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
         boolean bind_socket = prefs.getBoolean("bind_socket", false);
         if (bind_socket &&
@@ -639,20 +637,8 @@ public class EmailService implements AutoCloseable {
             //    throw new MailConnectException(
             //            new SocketConnectException("Debug", new IOException("Test"), host, port, 0));
 
-            String key = "dns." + host;
-            try {
-                main = DnsHelper.getByName(context, host, dnssec);
-                EntityLog.log(context, EntityLog.Type.Network, "Main address=" + main);
-                prefs.edit().putString(key, main.getHostAddress()).apply();
-            } catch (UnknownHostException ex) {
-                String last = prefs.getString(key, null);
-                if (TextUtils.isEmpty(last))
-                    throw ex;
-                else {
-                    EntityLog.log(context, EntityLog.Type.Network, "Using " + key + "=" + last);
-                    main = DnsHelper.getByName(context, last, dnssec);
-                }
-            }
+            main = DnsHelper.getByName(context, host, dnssec);
+            EntityLog.log(context, EntityLog.Type.Network, "Main address=" + main);
 
             boolean prefer_ip4 = prefs.getBoolean("prefer_ip4", true);
             if (prefer_ip4 && main instanceof Inet6Address) {

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

@@ -352,7 +352,6 @@ public class FragmentOptionsConnection extends FragmentBase implements SharedPre
         swDnsCustom.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
             @Override
             public void onCheckedChanged(CompoundButton buttonView, boolean checked) {
-                DnsHelper.clear(buttonView.getContext());
                 prefs.edit().putBoolean("dns_custom", checked).apply();
                 tvDnsExtra.setEnabled(checked || Build.VERSION.SDK_INT < Build.VERSION_CODES.Q);
                 etDnsExtra.setEnabled(checked || Build.VERSION.SDK_INT < Build.VERSION_CODES.Q);