diff --git a/src/AcaciaZPushPlugin/AcaciaZPushPlugin/Stubs/OutlookWrappers/StoresWrapper.cs b/src/AcaciaZPushPlugin/AcaciaZPushPlugin/Stubs/OutlookWrappers/StoresWrapper.cs
index 386952c..58dfd93 100644
--- a/src/AcaciaZPushPlugin/AcaciaZPushPlugin/Stubs/OutlookWrappers/StoresWrapper.cs
+++ b/src/AcaciaZPushPlugin/AcaciaZPushPlugin/Stubs/OutlookWrappers/StoresWrapper.cs
@@ -160,9 +160,12 @@ namespace Acacia.Stubs.OutlookWrappers
                 foreach (KeyValuePair<string, AccountWrapper> remove in removed)
                 {
                     Logger.Instance.Debug(this, "Account removed: {0} - {1}", remove.Value, remove.Key);
-                    _accountsBySmtp.Remove(remove.Value.SmtpAddress);
                     _accountsByStoreId.Remove(remove.Key);
-                    OnAccountRemoved(remove.Value);
+                    if (remove.Value != null)
+                    {
+                        _accountsBySmtp.Remove(remove.Value.SmtpAddress);
+                        OnAccountRemoved(remove.Value);
+                    }
                 }
             }
             catch (System.Exception e)
diff --git a/src/AcaciaZPushPlugin/AcaciaZPushPlugin/ZPush/ZPushWatcher.cs b/src/AcaciaZPushPlugin/AcaciaZPushPlugin/ZPush/ZPushWatcher.cs
index 3e19e51..c8afd5b 100644
--- a/src/AcaciaZPushPlugin/AcaciaZPushPlugin/ZPush/ZPushWatcher.cs
+++ b/src/AcaciaZPushPlugin/AcaciaZPushPlugin/ZPush/ZPushWatcher.cs
@@ -21,6 +21,7 @@ using Acacia.Utils;
 using Acacia.ZPush.Connect;
 using Microsoft.Win32;
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
@@ -227,7 +228,7 @@ namespace Acacia.ZPush
             }
         }
 
-        private readonly Dictionary<FolderRegistration, FolderWatcher> _folderWatchers = new Dictionary<FolderRegistration, FolderWatcher>();
+        private readonly ConcurrentDictionary<FolderRegistration, FolderWatcher> _folderWatchers = new ConcurrentDictionary<FolderRegistration, FolderWatcher>();
         private ZPushFolder _rootFolder;
 
         private void HandleFolderWatchers(ZPushAccount account)
@@ -245,7 +246,7 @@ namespace Acacia.ZPush
             if (!_folderWatchers.TryGetValue(folder, out watcher))
             {
                 watcher = new FolderWatcher();
-                _folderWatchers.Add(folder, watcher);
+                _folderWatchers.TryAdd(folder, watcher);
             }
 
             watcher.Discovered += handler;