My dear Name,
You will be glad to know that the marriage of my sister Raksha comes off on (month date). You are cordially invited to attend the function. The marriage party will come from Ambala on the (date and time). The reception will be held at our residence at (time) the next day. The bridegroom is a class I officer. We, therefore, Expect many high ranking officers to join the marriage party. We have decided to celebrate the marriage in a grand style.
I hope you will grace the occasion with your presence.
With best wishes,