diff --git a/OpenChange/MAPIStoreMailVolatileMessage.m b/OpenChange/MAPIStoreMailVolatileMessage.m
index 55d62309e..6c340a721 100644
--- a/OpenChange/MAPIStoreMailVolatileMessage.m
+++ b/OpenChange/MAPIStoreMailVolatileMessage.m
@@ -29,7 +29,6 @@
 #import <Foundation/NSData.h>
 #import <Foundation/NSDictionary.h>
 #import <Foundation/NSString.h>
-#import <Foundation/NSTimeZone.h>
 #import <Foundation/NSValue.h>
 #import <NGExtensions/NGHashMap.h>
 #import <NGExtensions/NSObject+Logs.h>
@@ -673,8 +672,6 @@ FillMessageHeadersFromProperties (NGMutableHashMap *headers,
   date = [mailProperties objectForKey: MAPIPropertyKey (PR_CLIENT_SUBMIT_TIME)];
   if (date)
     {
-      date = [date addYear: 0 month: 0 day: 0
-                      hour: 0 minute: 0 second: [[date timeZone] secondsFromGMT]];
       [headers addObject: [date rfc822DateString] forKey: @"date"];
     }
   [headers addObject: @"1.0" forKey: @"MIME-Version"];
diff --git a/OpenChange/MAPIStoreObject.m b/OpenChange/MAPIStoreObject.m
index 1c4b26be4..ecb00dba3 100644
--- a/OpenChange/MAPIStoreObject.m
+++ b/OpenChange/MAPIStoreObject.m
@@ -23,7 +23,6 @@
 #import <Foundation/NSArray.h>
 #import <Foundation/NSCalendarDate.h>
 #import <Foundation/NSDictionary.h>
-#import <Foundation/NSTimeZone.h>
 #import <NGExtensions/NSObject+Logs.h>
 #import <SOGo/SOGoObject.h>
 #import <SOGo/SOGoUser.h>
@@ -245,13 +244,8 @@ static Class NSExceptionK, MAPIStoreFolderK;
   struct SPropValue *cValue;
   NSUInteger counter;
   NSMutableDictionary *newProperties;
-  NSTimeZone *tz;
-  NSInteger tzOffset;
   id value;
 
-  tz = nil;
-  tzOffset = 0;
-
   newProperties = [NSMutableDictionary dictionaryWithCapacity: aRow->cValues];
   for (counter = 0; counter < aRow->cValues; counter++)
     {
@@ -268,16 +262,6 @@ static Class NSExceptionK, MAPIStoreFolderK;
                   @"attempting to set string property as PR_STRING8: %.8x",
                 cValue->ulPropTag];
           break;
-        case PT_SYSTIME:
-          if (!tz)
-            {
-              tz = [[self userContext] timeZone];
-              tzOffset = -[tz secondsFromGMT];
-            }
-          value = [value addYear: 0 month: 0 day: 0
-                            hour: 0 minute: 0 second: tzOffset];
-          [value setTimeZone: tz];
-          break;
         }
       [newProperties setObject: value
                         forKey: MAPIPropertyKey (cValue->ulPropTag)];
diff --git a/OpenChange/MAPIStoreTasksMessage.m b/OpenChange/MAPIStoreTasksMessage.m
index 9215bc409..20bf67f8b 100644
--- a/OpenChange/MAPIStoreTasksMessage.m
+++ b/OpenChange/MAPIStoreTasksMessage.m
@@ -367,13 +367,15 @@
   NSString *status, *priority, *tzName;
   NSCalendarDate *now;
   NSInteger tzOffset;
+  NSTimeZone *userTZ;
   double doubleValue;
 
   vToDo = [sogoObject component: YES secure: NO];
   vCalendar = [vToDo parent];
   [vCalendar setProdID: @"-//Inverse inc.//OpenChange+SOGo//EN"];
 
-  tzName = [[[self userContext] timeZone] name];
+  userTZ = [[self userContext] timeZone];
+  tzName = [userTZ name];
   tz = [iCalTimeZone timeZoneForName: tzName];
   [vCalendar addTimeZone: tz];
 
@@ -428,6 +430,13 @@
     {
       date = (iCalDateTime *) [vToDo uniqueChildWithTag: @"dtstart"];
       [date setTimeZone: tz];
+      /* The property is set to user's local time zone.
+         See: [MS-OXOTASK] 2.2.2.2.4
+         TODO: Ignore when the PT_SYSTIME is 0x5AE980E0*/
+      tzOffset = [userTZ secondsFromGMTForDate: value];
+      value = [value dateByAddingYears: 0 months: 0 days: 0
+                                 hours: 0 minutes: 0
+                               seconds: -tzOffset];
       [date setDateTime: value];
     }
   
@@ -437,6 +446,13 @@
     {
       date = (iCalDateTime *) [vToDo uniqueChildWithTag: @"due"];
       [date setTimeZone: tz];
+      /* The property is set to user's local time zone.
+         See: [MS-OXOTASK] 2.2.2.2.5
+         TODO: Ignore when the PT_SYSTIME is 0x5AE980E0*/
+      tzOffset = [userTZ secondsFromGMTForDate: value];
+      value = [value dateByAddingYears: 0 months: 0 days: 0
+                                 hours: 0 minutes: 0
+                               seconds: -tzOffset];
       [date setDateTime: value];
     }
 
@@ -445,7 +461,9 @@
   if (value)
     {
       date = (iCalDateTime *) [vToDo uniqueChildWithTag: @"completed"];
-      tzOffset = [[value timeZone] secondsFromGMTForDate: value];
+      /* The property is set to midnight in local time zone converted to UTC:
+         See: [MS-OXOTASK] 2.2.2.2.9 */
+      tzOffset = [userTZ secondsFromGMTForDate: value];
       value = [value dateByAddingYears: 0 months: 0 days: 0
                                  hours: 0 minutes: 0
                                seconds: -tzOffset];
diff --git a/OpenChange/MAPIStoreTypes.m b/OpenChange/MAPIStoreTypes.m
index 01b650463..76e72c5d6 100644
--- a/OpenChange/MAPIStoreTypes.m
+++ b/OpenChange/MAPIStoreTypes.m
@@ -119,6 +119,7 @@ NSObjectFromMAPISPropValue (const struct mapi_SPropValue *value)
       break;
     case PT_SYSTIME:
       result = [NSCalendarDate dateFromFileTime: &(value->value.ft)];
+      [result setTimeZone: utcTZ];
       break;
     case PT_BINARY:
     case PT_SVREID:
diff --git a/OpenChange/iCalEvent+MAPIStore.m b/OpenChange/iCalEvent+MAPIStore.m
index 40eb0c0ef..c5c70a686 100644
--- a/OpenChange/iCalEvent+MAPIStore.m
+++ b/OpenChange/iCalEvent+MAPIStore.m
@@ -207,16 +207,7 @@
   value
     = [properties objectForKey: MAPIPropertyKey (PidLidExceptionReplaceTime)];
   if (value)
-    {
-      if (!isAllDay)
-        {
-          tzOffset = [userTimeZone secondsFromGMTForDate: value];
-          value = [value dateByAddingYears: 0 months: 0 days: 0
-                                     hours: 0 minutes: 0
-                                   seconds: tzOffset];
-        }
-      [self setRecurrenceId: value];
-    }
+    [self setRecurrenceId: value];
  
   // start
   value = [properties objectForKey: MAPIPropertyKey (PidLidAppointmentStartWhole)];
@@ -241,13 +232,7 @@
           [start setTimeZone: nil];
         }
       else
-        {
-          tzOffset = [userTimeZone secondsFromGMTForDate: value];
-          value = [value dateByAddingYears: 0 months: 0 days: 0
-                                     hours: 0 minutes: 0
-                                   seconds: tzOffset];
           [start setDateTime: value];
-        }
     }
 
   /* end */
@@ -273,13 +258,7 @@
           [end setTimeZone: nil];
         }
       else
-        {
-          tzOffset = [[value timeZone] secondsFromGMTForDate: value];
-          value = [value dateByAddingYears: 0 months: 0 days: 0
-                                     hours: 0 minutes: 0
-                                   seconds: tzOffset];
           [end setDateTime: value];
-        }
     }
 
   /* priority */