Dovecot mail_location for fedora

What is the syntax for dovecot mail_location when postfix delivers mail to /var/spool/mail/?

These are the old unix style mbox, one file per user.

Not setting mail_location in 10-mail.conf results in Auto not finding it.

mbox: /var/spool/mail/%u said mbox root directory can't be a file.

mbox: /var/spool/mail/ tries to make Sent and Deleted Folders, etc.

maildir: /var/spool/mail/ closes the connection.

I am using Outlook 2016 and Thunderbird are two imap clients I am trying. For Dovecot, 2.2.31 is the version.

Postfix is version 3.2.2 and seems to be working.

A vanilla Fedora 26 is the OS