I defined a new global variable contact_recipients to hold the email address of the recipeint, change the invocation to read
{exp:email:contact_form redirect="3" user_recipients="false" recipients="{contact_recipients}" charset="utf-8"}and get back: “Your email had no valid recipients.” when I submit.
If I place {contact_recipients} as text inside the email form it seems to have the correct value.
Am I doing anything wrong?