Beat me to it. Why isn’t every unsolicited pitch without an unsubscribe link immediately blocked/marked as spam?
Not to mention the obviously unrelated-to-publishing, dodgy sounding email addresses. Red flag #1 where only a single red flag is needed to discard it.
Having said that, less technically minded people, as authors may be, may not even notice that.
Is the presence of an unsubscribe link a useful signal? I presume that just marks your email address as active in the spammer's database.