It seems like there's a problem with the "Mail Alert" module that's causing it to trigger multiple email alerts when you update a product with zero stock.
Can anyone replicate this issue with the latest version of the module on PS 1.7? you take a product that has 0 stock, open the product page in the admin so you can edit it, then save the product, so as you save it you'll receive many emails from the Mail Alert (that you need to previously have configured to send stock alerts when stock level of a product reaches Zero).
Also try products with combinations . I've had this issue when a product with combinations has some combinations with stock and some without. Also I've noticed that for a product with combinations, when at least 1 combination does not have stock, every time a customer orders one of the other combinations I get the email alert.
Thanks