Agent etiquette

Hi. I'm new to all of this - submitting my stuff to agents and connecting with other writer type people.

I just received a fantastic rejection letter from Katie Kotchman at the Don Congdon agency. What's the accepted etiquette as far as replying to her to thank her for the encouragment?

Thanks, Renee and Cyia. I'll do that, and I think that when I finish the novel I'm working on, she'll be the first agent I submit to.