Who was Varys writing to?
And was he trying to poison Dany?
shareHe's telling Jon's true parentage and how Ned hid him. It looked like he already had several messages written and wrapped, ready to send by raven. So probably to the surviving great houses.
I would say yes, he was trying to poison her. The little girl works in the kitchen and when she says "She's not eating." Varys says "We'll try again at supper." Could be something else, but I doubt it.
Also, I think most of the messages got out. When they come to arrest him, he burns the one he's writing, but the other scrolls that were on the table earlier are gone.