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Not yet, I will let you know once we received it. is the most popular phrase on the web.

Not yet, I will let you know when we receive it. 11,710,000,000 results on the web	Not yet, I will let you know once we received it. 12,420,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
I will let you know when it is finished. And I will let you know when I'm ready to look at them. Well, I will let you know when the king is back. I will let you know when I'm joking. But I will let you know when you cracked the case. No, not yet, but I'll let you know when I do. I will let you know when a good time is. I promise. I will let you know when and how I will collect him.	Now, as soon as I can figure out a way to move her off the investigation, I will let you know. And when I have curried favor with her, I will let you know. That's all I can remember, Mom, but if I think of any more, I will let you know. Okay, I will talk it over with my staff and I will let you know. As soon as I have his head in a box, I will let you know. If I find anything more, I will let you know. Well, I will let you know when the king is back. If I get a lead on your brother, I will let you know.

Not yet, I will let you know when we receive it.

11,710,000,000 results on the web

Not yet, I will let you know once we received it.

12,420,000,000 results on the web

More popular!

Now, as soon as I can figure out a way to move her off the investigation, I will let you know.
And when I have curried favor with her, I will let you know.
That's all I can remember, Mom, but if I think of any more, I will let you know.
Okay, I will talk it over with my staff and I will let you know.
As soon as I have his head in a box, I will let you know.
If I find anything more, I will let you know.
Well, I will let you know when the king is back.
If I get a lead on your brother, I will let you know.