Possible to not close window when user clicks on submit

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Hi Pete,

I like your plugin and think it's well thought out.
But I would like the window to stay open when a user clicks on submit.
Is there a way to do it?

The reason I want this, is because after submission, I show the user a message that says: Please check your email etc. And it's also useful if a user does not enter a valid address (I am not checking this via js).

Any feedback appreciated.
Cheers
Stefan