Suddenly Not getting email notifications after an order

First, what version of Zen Cart are you using?

Second, have you talked to your host?

Zen Cart doesn't just stop doing things, either the hosting has changed, or the code has been changed or an Admin setting has changed - all of which need human intervention somewhere.

I had the same problem. Everything worked fine until a couple of days ago, I started receiving payments but no invoices. Customers were able to download their purchases so it was just Admin not getting invoices for the sales. No changes were made to the Admin section and I am using version v1.5.0.

I solved my problem when I accidentally came across the Mail Settings in Zencart and noticed that the password was wrong. I realized right then and there that the Password for the Email Account used in ZC had been changed by me and failed to enter the new password in ZC. If this is your problem, go to Configuration->Email Options->SMTP Email Account Password and enter the new one. After I corrected that, I placed an order and I got my new invoice. I hope this helps someone else because I spent a whole day researching it and nothing I found worked.