General IMAP question

[Scott Techlist]

Software is Centos7, Dovecot 2.2.10

>Use that single mailbox with IMAP, others stay to POP

Thanks, I considered that and looked up the ways to restrict IMAP access.  But:

How will the IMAP account behave with the current mail_location setting below?  

mail_location = mbox:~/mail:INBOX=/var/mail/%u

That is, where will the IMAP account's mail "go"?  Right now it goes to /var/mail/[localusername].  Maybe incorrectly, I assumed IMAP required Maildir format?  How are folders handled with this setting?.  The one IMAP account would be used for spamassassin training, it would need 2 shared/public folders ("spam", "ham").