bsd-from

Show who has sent mail to your mailbox

$ bsd-from

$ bsd-from -c

$ bsd-from -s [sender]

$ bsd-from -f [path/to/mailbox]

$ bsd-from [username]

bsd-from [-c] [-f file] [-s sender] [user]

bsd-from (also known as from) prints the mail header lines from a mailbox, showing the names of people who have sent mail. By default, it examines the invoker's mailbox.
The command provides a quick way to see pending mail without opening a full mail client. It displays the "From" lines of messages, giving an overview of who has sent mail.

-c

Print only a count of messages and exit

Examine the specified file instead of the default mailbox. Use - to read from standard input

Only print mail from addresses containing the specified string

Examine the specified user's mailbox instead of the invoker's (requires appropriate privileges)

When using the -f option, the user argument should not be specified. Examining other users' mailboxes requires elevated privileges.
The default mailbox location is determined by the MAIL environment variable, or /var/mail if not set.

The from command first appeared in BSD 3.0 in 1979 as part of the Berkeley Software Distribution mail utilities.

biff(1), mail(1)