It's a small change, but worthwhile... the two RRULES are altered only.
/opt/zimbra/conf# vi timezones.ics
BEGIN:VTIMEZONE
TZID

GMT+10.00) Canberra / Melbourne / Sydney
LAST-MODIFIED:20070209T005655Z
BEGIN:STANDARD
DTSTART:19710101T030000
TZOFFSETTO:+1000
TZOFFSETFROM:+1100
RRULE:FREQ=YEARLY;WKST=MO;INTERVAL=1;BYMONTH=4;BYD AY=1SU
END:STANDARD
BEGIN

AYLIGHT
DTSTART:19710101T020000
TZOFFSETTO:+1100
TZOFFSETFROM:+1000
RRULE:FREQ=YEARLY;WKST=MO;INTERVAL=1;BYMONTH=10;BY DAY=1SU
END

AYLIGHT
END:VTIMEZONE