Hi @IBrockschmidt ,
When you say preferred email, do you mean our default email property?
If yes, then we could trigger a workflow using this- the only tricky part would be ensuring that only contacts who change their email address are enrolled as if we set it to just “email is known”, it will enroll contacts whenever an update to is made- i.e. when new contacts are created.
Hope this helps!
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Thanks and Regards.