[jggimi]

Disclaimer: I don't use mail(1). My preference is for the mutt package.

The mail(1) man page refers to the "Mail Reference Manual". Google searching provided a link to it here: https://docs.freebsd.org/44doc/usd/07.mail/paper.pdf

1. Using the link above, I learned that you can use & f .-$ to list all messages.
2. The man page states that you can "delete (d) or reply (r) to it."
3. This is well outside the scope of a Mail User Agent (MUA) such as mail(1). It requires provisioning a Mail Transfer Agent (MTA), commonly called a "mail server." This requires static IP address(es) on the Internet, purchased domain names, provisioning DNS records, a whole lot of knowledge about the protocols SMTP, ESMTP, SPF, and DMARC, managing the reputation(s) of your IP address(es), and most importantly -- avoiding any provisioning errors that allows your server to be attacked and become a spam pump. There is a built-in mail server, smtpd(8), which in its default configuration doesn't accept incoming mail from the network and is used only to manage local mail.