Which of the following is the appropriate format of the URL of an email?

An email address places a username before the @ sign and the mail domain after it, a shape that www@mail.com follows.

www_mail.com joins the parts with an underscore and has no @, so it cannot route mail.

WWW@mail.com forces the local part into capitals, which is treated as unconventional here.

www.mail.com uses a dot in place of @ and reads as a website name, not a mailbox.

The @ sign is what separates the recipient's name from the server that holds the mailbox.

Domain names to the right of @ are case-insensitive, while the left part can be case-sensitive.