C# - Keep The Content After Postback?

I have a ASPX page, on this page there are two dropdown list, one button and one gridview. When the pages is loaded,these two dropdown would bind data from sql server. Then you select items from these two dropdown list, then click Button A to get data from sql server based on these two dropdown list, rendering the data using gridview. There is another Button, Button B. Then I click the Button B to do something, like send mail. But the page becomes the first time it's loaded, the content disappeared after postback. How can I keep the content after I click the Button B?

void SendInvitationMail_Click(object sender, EventArgs e)
{
send mail here
}
void QueryButton_Click(object sender, EventArgs e)

[Code]....

After I click the Query Button, it would get bind the data to gridview, then I click the Send Mail button. I want to keep all the result even I click the Send Mail button.