diff --git a/app/src/main/java/eu/faircode/email/ServiceSynchronize.java b/app/src/main/java/eu/faircode/email/ServiceSynchronize.java
index db6c27e9fb..a2daac517e 100644
--- a/app/src/main/java/eu/faircode/email/ServiceSynchronize.java
+++ b/app/src/main/java/eu/faircode/email/ServiceSynchronize.java
@@ -1122,26 +1122,9 @@ public class ServiceSynchronize extends ServiceBase implements SharedPreferences
 
                                 db.operation().liveOperations(folder.id).observe(cowner, new Observer<List<TupleOperationEx>>() {
                                     private List<Long> handling = new ArrayList<>();
-                                    private final PowerManager.WakeLock wlFolder = pm.newWakeLock(
-                                            PowerManager.PARTIAL_WAKE_LOCK, BuildConfig.APPLICATION_ID + ":folder." + folder.id);
 
-                                    @Override
-                                    public void onChanged(final List<TupleOperationEx> _operations) {
-                                        List<Long> ops = new ArrayList<>();
-                                        List<TupleOperationEx> submit = new ArrayList<>();
-                                        for (TupleOperationEx op : _operations) {
-                                            if (!handling.contains(op.id))
-                                                submit.add(op);
-                                            ops.add(op.id);
-                                        }
-                                        handling = ops;
-
-                                        if (submit.size() > 0) {
-                                            Log.i(folder.name + " queuing operations=" + submit.size() +
-                                                    " init=" + folder.initialize + " poll=" + folder.poll);
-
-                                            // Partition operations by priority
-                                            Map<TupleOperationEx.PartitionKey, List<TupleOperationEx>> partitions = new TreeMap<>(new Comparator<TupleOperationEx.PartitionKey>() {
+                                    private final Map<TupleOperationEx.PartitionKey, List<TupleOperationEx>> partitions =
+                                            new TreeMap<>(new Comparator<TupleOperationEx.PartitionKey>() {
                                                 @Override
                                                 public int compare(TupleOperationEx.PartitionKey k1, TupleOperationEx.PartitionKey k2) {
                                                     Integer p1 = k1.getPriority();
@@ -1150,17 +1133,47 @@ public class ServiceSynchronize extends ServiceBase implements SharedPreferences
                                                 }
                                             });
 
+                                    private final PowerManager.WakeLock wlFolder = pm.newWakeLock(
+                                            PowerManager.PARTIAL_WAKE_LOCK, BuildConfig.APPLICATION_ID + ":folder." + folder.id);
+
+                                    @Override
+                                    public void onChanged(final List<TupleOperationEx> _operations) {
+                                        // Get new operations
+                                        List<Long> ops = new ArrayList<>();
+                                        List<TupleOperationEx> added = new ArrayList<>();
+                                        for (TupleOperationEx op : _operations) {
+                                            if (!handling.contains(op.id))
+                                                added.add(op);
+                                            ops.add(op.id);
+                                        }
+                                        handling = ops;
+
+                                        if (added.size() > 0) {
+                                            Log.i(folder.name + " queuing operations=" + added.size() +
+                                                    " init=" + folder.initialize + " poll=" + folder.poll);
+
+                                            // Partition operations by priority
                                             boolean offline = (mapFolders.get(folder) == null);
-                                            for (TupleOperationEx op : submit) {
-                                                TupleOperationEx.PartitionKey key = op.getPartitionKey(offline);
-                                                if (!partitions.containsKey(key))
-                                                    partitions.put(key, new ArrayList<>());
-                                                partitions.get(key).add(op);
+                                            List<TupleOperationEx.PartitionKey> keys = new ArrayList<>();
+                                            synchronized (partitions) {
+                                                for (TupleOperationEx op : added) {
+                                                    TupleOperationEx.PartitionKey key = op.getPartitionKey(offline);
+
+                                                    if (!partitions.containsKey(key)) {
+                                                        partitions.put(key, new ArrayList<>());
+                                                        keys.add(key);
+                                                    }
+
+                                                    partitions.get(key).add(op);
+                                                }
                                             }
 
-                                            for (TupleOperationEx.PartitionKey key : partitions.keySet()) {
-                                                List<TupleOperationEx> partition = partitions.get(key);
-                                                Log.i(folder.name + " queuing operations=" + partition.size() + " key=" + key);
+                                            for (TupleOperationEx.PartitionKey key : keys) {
+                                                synchronized (partitions) {
+                                                    Log.i(folder.name +
+                                                            " queuing partition=" + key +
+                                                            " operations=" + partitions.get(key).size());
+                                                }
 
                                                 executor.submit(new Helper.PriorityRunnable(key.getPriority()) {
                                                     @Override
@@ -1168,7 +1181,16 @@ public class ServiceSynchronize extends ServiceBase implements SharedPreferences
                                                         super.run();
                                                         try {
                                                             wlFolder.acquire();
-                                                            Log.i(folder.name + " process");
+
+                                                            List<TupleOperationEx> partition;
+                                                            synchronized (partitions) {
+                                                                partition = partitions.get(key);
+                                                                partitions.remove(key);
+                                                            }
+
+                                                            Log.i(folder.name +
+                                                                    " executing partition=" + key +
+                                                                    " operations=" + partition.size());
 
                                                             // Get folder
                                                             Folder ifolder = mapFolders.get(folder); // null when polling