Dear ________ (name),
Greetings of the day!
This is informed you that the office will be closed for ____ (number of days) from __/__/_____ (date) till __/__/_____ (date) on __________ (on the occasion of/ reason being).
It is to state that the office will be reopening from __/__/_____ (date) onwards and shall be operational as per the schedule decided.
Thanks & Regards,
_________ (Contact details)