How to set up so I can reply email from the same email address it was received

I use gmail and have several alias for different function of my work. How can I set up mail so I can reply email from the same email address the mail was received?

I can reply from the same email address using gmail web service but not able to do so in Mac Mail. I have a couple alias where I am able to do so but I cannot recall how I set those up initially.