diff --git a/src/java/davmail/exchange/ExchangeSession.java b/src/java/davmail/exchange/ExchangeSession.java
index 67bd8c13..11ad4dd2 100644
--- a/src/java/davmail/exchange/ExchangeSession.java
+++ b/src/java/davmail/exchange/ExchangeSession.java
@@ -3128,6 +3128,11 @@ public abstract class ExchangeSession {
      * @throws IOException on error
      */
     public FreeBusy getFreebusy(String attendee, String startDateValue, String endDateValue) throws IOException {
+        // first check that email address is valid to avoid InvalidSmtpAddress error
+        if (attendee == null || attendee.indexOf('@') < 0 || attendee.charAt(attendee.length() - 1) == '@') {
+            return null;
+        }
+        
         attendee = replaceIcal4Principal(attendee);
         if (attendee.startsWith("mailto:") || attendee.startsWith("MAILTO:")) {
             attendee = attendee.substring("mailto:".length());
diff --git a/src/java/timezones.properties b/src/java/timezones.properties
index bd48fe58..fc33440e 100644
--- a/src/java/timezones.properties
+++ b/src/java/timezones.properties
@@ -93,4 +93,5 @@ GMT\ -0500\ (Standard)\ /\ GMT\ -0400\ (Daylight)=America/New_York
 GMT\ -0600\ (Standard)\ /\ GMT\ -0500\ (Daylight)=America/Chicago
 GMT\ -0700\ (Standard)\ /\ GMT\ -0600\ (Daylight)=America/Denver
 GMT\ -0800\ (Standard)\ /\ GMT\ -0700\ (Daylight)=America/Los_Angeles
-GMT\ Standard\ Time=GMT Standard Time
\ No newline at end of file
+GMT\ Standard\ Time=GMT Standard Time
+Greenwich\ Standard\ Time=Greenwich Standard Time