3.16 Can I use sendmail 8.9.3 as either IMAP or POP3 server?

Sendmail is an SMTP server (Mail Transfer Agent -or- MTA). It accepts mail from clients and delivers it to other servers. IMAP and POP3 are protocols used by clients to download mail from servers. In short they are two very different but related things. Red Hat Linux comes with IMAP/POP3 daemons. See the answer to question 3.9 for more information.