Why isn't my store discount code limiting purchases as intended?

[608Threads]

Hello,

We have a discount code setup for a corporate client's online store that isn't working as planned. They're offering 2 free t-shirt options (unisex & women's) to all their employees. We want the discount code to only be used one time per customer (email address), but it's allowing shoppers to use the code for both style shirts, and more than one shirt at a time per purchase. 

We're hoping it's a quick fix, any help is appreciated!

Thank you,

Jason @608 Threads