diff --git a/FAQ.md b/FAQ.md
index bc2ddee8..be789620 100644
--- a/FAQ.md
+++ b/FAQ.md
@@ -11,7 +11,8 @@ Frequently Asked Questions
 * View network connections (ACCESS_NETWORK_STATE): to monitor internet connectivity changes
 * Run at startup (RECEIVE_BOOT_COMPLETED): to start monitoring on device start
 * Optional: read your contacts (READ_CONTACTS): to autocomplete addresses
-* ... (FOREGROUND_SERVICE): to run a foreground service on Android 9 Pie and later, see also the next question.
+* ... (BILLING): to offer in-app purchases
+* ... (FOREGROUND_SERVICE): to run a foreground service on Android 9 Pie and later, see also the next question
 
 <a name="FAQ2"></a>
 **(2) Why is there a permanent notification shown?**
diff --git a/app/build.gradle b/app/build.gradle
index 79deb3ba..2551904e 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -55,6 +55,8 @@ dependencies {
     // https://mvnrepository.com/artifact/androidx.room/room-runtime
     // https://mvnrepository.com/artifact/androidx.paging/paging-runtime
 
+    // https://developer.android.com/google/play/billing/billing_library_releases_notes
+
     // https://javaee.github.io/javamail/
     // https://jsoup.org/
     // http://www.freeutils.net/source/jcharset/
@@ -70,6 +72,7 @@ dependencies {
     def lifecycle_version = "2.0.0-rc01"
     def room_version = "2.0.0-rc01"
     def paging_version = "2.0.0-rc01"
+    def billingclient_version = "1.1"
     def javamail_version = "1.6.0"
     def jsoup_version = "1.11.3"
     def jcharset_version = "2.0"
@@ -88,6 +91,8 @@ dependencies {
 
     implementation "androidx.paging:paging-runtime:$paging_version"
 
+    implementation "com.android.billingclient:billing:$billingclient_version"
+
     implementation "com.sun.mail:android-mail:$javamail_version"
     implementation "com.sun.mail:android-activation:$javamail_version"
 
diff --git a/app/proguard-rules.pro b/app/proguard-rules.pro
index 251617c0..0752a1ec 100644
--- a/app/proguard-rules.pro
+++ b/app/proguard-rules.pro
@@ -27,6 +27,9 @@
 #AndroidX
 -keep class androidx.appcompat.app.AppCompatViewInflater { <init>(...); }
 
+#IAB
+-keep class com.android.vending.billing.**
+
 #JavaMail
 -dontshrink
 -keep class javax.** {*;}
diff --git a/app/src/main/AndroidManifest.xml b/app/src/main/AndroidManifest.xml
index fdac5dbf..028edcc5 100644
--- a/app/src/main/AndroidManifest.xml
+++ b/app/src/main/AndroidManifest.xml
@@ -7,6 +7,7 @@
     <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
     <uses-permission android:name="android.permission.READ_CONTACTS" />
     <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
+    <uses-permission android:name="com.android.vending.BILLING" />
 
     <application
         android:name=".ApplicationEx"
diff --git a/app/src/main/java/eu/faircode/email/ActivityView.java b/app/src/main/java/eu/faircode/email/ActivityView.java
index dd339f08..93f21c92 100644
--- a/app/src/main/java/eu/faircode/email/ActivityView.java
+++ b/app/src/main/java/eu/faircode/email/ActivityView.java
@@ -29,6 +29,7 @@ import android.content.res.Configuration;
 import android.net.Uri;
 import android.os.Build;
 import android.os.Bundle;
+import android.os.Handler;
 import android.os.ParcelFileDescriptor;
 import android.preference.PreferenceManager;
 import android.provider.Settings;
@@ -44,6 +45,11 @@ import android.widget.ListView;
 import android.widget.TextView;
 import android.widget.Toast;
 
+import com.android.billingclient.api.BillingClient;
+import com.android.billingclient.api.BillingClientStateListener;
+import com.android.billingclient.api.BillingFlowParams;
+import com.android.billingclient.api.Purchase;
+import com.android.billingclient.api.PurchasesUpdatedListener;
 import com.google.android.material.snackbar.Snackbar;
 
 import java.io.BufferedReader;
@@ -72,11 +78,12 @@ import androidx.lifecycle.Lifecycle;
 import androidx.lifecycle.Observer;
 import androidx.localbroadcastmanager.content.LocalBroadcastManager;
 
-public class ActivityView extends ActivityBase implements FragmentManager.OnBackStackChangedListener {
+public class ActivityView extends ActivityBase implements FragmentManager.OnBackStackChangedListener, PurchasesUpdatedListener {
     private View view;
     private DrawerLayout drawerLayout;
     private ListView drawerList;
     private ActionBarDrawerToggle drawerToggle;
+    private BillingClient billingClient;
 
     private boolean newIntent = false;
 
@@ -307,6 +314,9 @@ public class ActivityView extends ActivityBase implements FragmentManager.OnBack
             }
         }.load(this, new Bundle());
 
+        billingClient = BillingClient.newBuilder(this).setListener(this).build();
+        billingClient.startConnection(billingClientStateListener);
+
         checkIntent(getIntent());
     }
 
@@ -349,6 +359,9 @@ public class ActivityView extends ActivityBase implements FragmentManager.OnBack
             newIntent = false;
             getSupportFragmentManager().popBackStack("unified", 0);
         }
+
+        if (billingClient.isReady())
+            queryPurchases();
     }
 
     @Override
@@ -366,6 +379,7 @@ public class ActivityView extends ActivityBase implements FragmentManager.OnBack
 
     @Override
     protected void onDestroy() {
+        billingClient.endConnection();
         super.onDestroy();
     }
 
@@ -518,8 +532,22 @@ public class ActivityView extends ActivityBase implements FragmentManager.OnBack
     }
 
     private void onMenuPro() {
-        if (Helper.isPlayStoreInstall(this)) {
+        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
+        if (prefs.getBoolean("pro", false)) {
+            Snackbar.make(view, R.string.title_pro_activated, Snackbar.LENGTH_LONG).show();
+            return;
+        }
 
+        if (Helper.isPlayStoreInstall(this)) {
+            BillingFlowParams flowParams = BillingFlowParams.newBuilder()
+                    .setSku(BuildConfig.APPLICATION_ID + ".pro")
+                    .setType(BillingClient.SkuType.INAPP)
+                    .build();
+            int responseCode = billingClient.launchBillingFlow(ActivityView.this, flowParams);
+            String text = Helper.getBillingResponseText(responseCode);
+            Log.i(Helper.TAG, "IAB launch billing flow response=" + text);
+            if (responseCode != BillingClient.BillingResponse.OK)
+                Snackbar.make(view, text, Snackbar.LENGTH_LONG).show();
         } else
             startActivity(getIntentPro());
     }
@@ -755,4 +783,68 @@ public class ActivityView extends ActivityBase implements FragmentManager.OnBack
             }.load(this, args);
         }
     }
+
+    private BillingClientStateListener billingClientStateListener = new BillingClientStateListener() {
+        private int backoff = 4; // seconds
+
+        @Override
+        public void onBillingSetupFinished(@BillingClient.BillingResponse int responseCode) {
+            String text = Helper.getBillingResponseText(responseCode);
+            Log.i(Helper.TAG, "IAB connected response=" + text);
+            if (responseCode == BillingClient.BillingResponse.OK) {
+                backoff = 4;
+                queryPurchases();
+            } else
+                Snackbar.make(view, text, Snackbar.LENGTH_LONG).show();
+        }
+
+        @Override
+        public void onBillingServiceDisconnected() {
+            backoff *= 2;
+            Log.i(Helper.TAG, "IAB disconnected retry in " + backoff + " s");
+            new Handler().postDelayed(new Runnable() {
+                @Override
+                public void run() {
+                    if (!billingClient.isReady())
+                        billingClient.startConnection(billingClientStateListener);
+                }
+            }, backoff * 1000L);
+        }
+    };
+
+    @Override
+    public void onPurchasesUpdated(int responseCode, @android.support.annotation.Nullable List<Purchase> purchases) {
+        String text = Helper.getBillingResponseText(responseCode);
+        Log.i(Helper.TAG, "IAB purchases updated response=" + text);
+        if (responseCode == BillingClient.BillingResponse.OK)
+            checkPurchases(purchases);
+        else
+            Snackbar.make(view, text, Snackbar.LENGTH_LONG).show();
+    }
+
+    private void queryPurchases() {
+        Purchase.PurchasesResult result = billingClient.queryPurchases(BillingClient.SkuType.INAPP);
+        String text = Helper.getBillingResponseText(result.getResponseCode());
+        Log.i(Helper.TAG, "IAB query purchases response=" + text);
+        if (result.getResponseCode() == BillingClient.BillingResponse.OK)
+            checkPurchases(result.getPurchasesList());
+        else
+            Snackbar.make(view, text, Snackbar.LENGTH_LONG).show();
+    }
+
+    private void checkPurchases(List<Purchase> purchases) {
+        if (purchases != null) {
+            SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
+            SharedPreferences.Editor editor = prefs.edit();
+            editor.remove("pro");
+            for (Purchase purchase : purchases) {
+                Log.i(Helper.TAG, "IAB SKU=" + purchase.getSku());
+                if ((BuildConfig.APPLICATION_ID + ".pro").equals(purchase.getSku())) {
+                    editor.putBoolean("pro", true);
+                    Log.i(Helper.TAG, "IAB pro features activated");
+                }
+            }
+            editor.apply();
+        }
+    }
 }
diff --git a/app/src/main/java/eu/faircode/email/Helper.java b/app/src/main/java/eu/faircode/email/Helper.java
index eb12f8d1..0e106335 100644
--- a/app/src/main/java/eu/faircode/email/Helper.java
+++ b/app/src/main/java/eu/faircode/email/Helper.java
@@ -31,6 +31,7 @@ import android.widget.EditText;
 import android.widget.ImageView;
 import android.widget.Spinner;
 
+import com.android.billingclient.api.BillingClient;
 import com.google.android.material.bottomnavigation.BottomNavigationView;
 
 import java.io.BufferedReader;
@@ -188,4 +189,55 @@ public class Helper {
             sb.append(String.format("%02x", b));
         return sb.toString();
     }
+
+    static String getBillingResponseText(@BillingClient.BillingResponse int responseCode) {
+        switch (responseCode) {
+            case BillingClient.BillingResponse.BILLING_UNAVAILABLE:
+                // Billing API version is not supported for the type requested
+                return "BILLING_UNAVAILABLE";
+
+            case BillingClient.BillingResponse.DEVELOPER_ERROR:
+                // Invalid arguments provided to the API.
+                return "DEVELOPER_ERROR";
+
+            case BillingClient.BillingResponse.ERROR:
+                // Fatal error during the API action
+                return "ERROR";
+
+            case BillingClient.BillingResponse.FEATURE_NOT_SUPPORTED:
+                // Requested feature is not supported by Play Store on the current device.
+                return "FEATURE_NOT_SUPPORTED";
+
+            case BillingClient.BillingResponse.ITEM_ALREADY_OWNED:
+                // Failure to purchase since item is already owned
+                return "ITEM_ALREADY_OWNED";
+
+            case BillingClient.BillingResponse.ITEM_NOT_OWNED:
+                // Failure to consume since item is not owned
+                return "ITEM_NOT_OWNED";
+
+            case BillingClient.BillingResponse.ITEM_UNAVAILABLE:
+                // Requested product is not available for purchase
+                return "ITEM_UNAVAILABLE";
+
+            case BillingClient.BillingResponse.OK:
+                // Success
+                return "OK";
+
+            case BillingClient.BillingResponse.SERVICE_DISCONNECTED:
+                // Play Store service is not connected now - potentially transient state.
+                return "SERVICE_DISCONNECTED";
+
+            case BillingClient.BillingResponse.SERVICE_UNAVAILABLE:
+                // Network connection is down
+                return "SERVICE_UNAVAILABLE";
+
+            case BillingClient.BillingResponse.USER_CANCELED:
+                // User pressed back or canceled a dialog
+                return "USER_CANCELED";
+
+            default:
+                return Integer.toString(responseCode);
+        }
+    }
 }
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 4ea3d588..780adf4b 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -176,6 +176,7 @@
     <string name="title_legend_connected">Connected</string>
     <string name="title_legend_closing">Closing</string>
 
+    <string name="title_pro_activated">All pro features are activated</string>
     <string name="title_pro_valid">All pro features activated</string>
     <string name="title_pro_invalid">Invalid response</string>