Hello, and welcome back to Just Answer.
I can understand your frustration. Typically, and unfortunately for first time authors, there will be no response or acknowledgement after receiving the email or even the requested submissions of attachments, unless they are interested, and this could take weeks or months to receive. If they replied to every email they got from aspiring authors, there would be no time to do anything else.
It's been my experience that they will ask for the first chapter or the first few chapters, to decide if the book is worth consideration for publishing. I'm assuming this is what you're referring to, when you mentioned 'attachments'.
It's not a waste of time, as long as you're getting information about your book into the hands of literary agents and publishers for consideration. I would suggest following up the email with a hard copy of the first chapter or whatever their guidelines call for, by regular mail. You can send it return receipt, so you get proof it was received.
I wish you much good luck and hope you will soon get a sign of interest in your book from one of your submissions!
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