diff --git a/src/java/davmail/exchange/ExchangeSession.java b/src/java/davmail/exchange/ExchangeSession.java
index 5bf02e5a..88f3e3a1 100644
--- a/src/java/davmail/exchange/ExchangeSession.java
+++ b/src/java/davmail/exchange/ExchangeSession.java
@@ -3304,7 +3304,7 @@ public abstract class ExchangeSession {
      * @param folderPath absolute folder path
      * @return true if folderPath is a public or shared folder
      */
-    public abstract boolean isMainCalendar(String folderPath);
+    public abstract boolean isMainCalendar(String folderPath) throws IOException;
 
     static final String MAILBOX_BASE = "/cn=";
 
diff --git a/src/java/davmail/exchange/ews/EwsExchangeSession.java b/src/java/davmail/exchange/ews/EwsExchangeSession.java
index fad20447..064a3dc7 100644
--- a/src/java/davmail/exchange/ews/EwsExchangeSession.java
+++ b/src/java/davmail/exchange/ews/EwsExchangeSession.java
@@ -1715,7 +1715,7 @@ public class EwsExchangeSession extends ExchangeSession {
                     createOrUpdateItemMethod.setTimezoneContext(EwsExchangeSession.this.getVTimezone().getPropertyValue("TZID"));
                 }
                 //}
-            }
+                }
             executeMethod(createOrUpdateItemMethod);
 
             itemResult.status = createOrUpdateItemMethod.getStatusCode();
@@ -2160,8 +2160,10 @@ public class EwsExchangeSession extends ExchangeSession {
     }
 
     @Override
-    public boolean isMainCalendar(String folderPath) {
-        return "calendar".equalsIgnoreCase(folderPath) || (currentMailboxPath + "/calendar").equalsIgnoreCase(folderPath);
+    public boolean isMainCalendar(String folderPath) throws IOException {
+        FolderId currentFolderId = getFolderId(folderPath);
+        FolderId calendarFolderId = getFolderId("calendar");
+        return calendarFolderId.name.equals(currentFolderId.name) && calendarFolderId.value.equals(currentFolderId.value);
     }
 
     @Override