new install, save first form with no changes and get error

I have installed the plugin, first time.
There is a ready made form. If I make no changes other than to save the form, it shows an errorInvalid mailbox syntax is used.straight away.
This is the form prepared by the plugin, so how can this be?
It is using the email address from the Administration Email Address as expected and is correctly wrapped in <>; the address is admin@my domain.

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