I don't use POP3 with Mail, but perhaps this first blank e-mail is a "header" e-mail (like on a spreadsheet). It only shows the order of the information that will be displayed in the following e-mails.
On a Mac since 1984. Currently: 24" M1 iMac, M2 Pro Mac mini with 27" BenQ monitor, M2 Macbook Air, MacOS 14.x; iPhones, iPods (yes, still) and iPads.
