... Leaving the filed blank doesn't work obviously, nor does typing "(no sender)".
Header 1 Header 2 Header 3 From Does not contain @
A valid email address must contain a @ character, right?
Same logic applies to a . (dot) character if you want to try that. I have never seen an email address not in the form firstname.lastname@example.org
Let me know if this works. I don't know how to send an email to myself with nothing in the "from" field so I can't test it. Not clever or scummy enough I suppose.