I have the same issue.
I have created a dynamichidden field for obtaining the email address of the author of the post.
At the moment i have not yet written the code to get it, so it looks like this:
[dynamichidden email “[email protected]”]
However when i try to use [email] in the “to” field i get the same mailbox syntax error.
How do we make dynamichidden or dynamictext fields compatible with the mailbox syntax?