Thunderbird mac always send return receipts even after i set "never send"

Question

I am using Thunderbird mac 17.0.7, it always send "return receipts" even I have set the "Never send a return receipt". It did act as expected, but i don't know when and why it become so. I have check the global setting and the account setting, it does be "Never send a return receipt". Any ideas? Thanks!

Answer 1

If your server is Exchange, it's a feature.