First, please note my corrections above. You must capitalise the first word of every sentence and always capitalise the word "I". Also, starting with "I would like to know" means your sentence was not a question so no question mark was needed at the end.
I'm not sure there is an official correct position for it. I would probably write something like:
Dear Mr Smith
Very urgent - latest report on sales
I am writing to advise that the May sales report has been severely delayed by an IT failure. We hope to be able to produce it by the end of June.