Выражение встречается в следующем контексте:
Dear Mr. ...,

This letter is to inform you that the mandate of OOO "......" is completed as of today.
You can prepare your final invoice that will be paid according to the terms of your contract.
If we have any other question concerning the work performed by OOO "......" we will contact you.

Yours truly,

Заранее спасибо