まず、この辺注意
cyrus-sasl-devel
cyrus-sasl-md5
cyrus-sasl-plain

/etc/dovecot/dovecot.conf を編集
変更 ( IPv6をリスンしない場合 )

listen = *

/etc/dovecot/conf.d/10-auth.confを編集

disable_plaintext_auth = no
auth_mechanisms =  plain login

/etc/dovecot/conf.d/10-mail.confを編集

mail_location = maildir:~/Maildir

/etc/dovecot/conf.d/10-master.conf を編集
# Postfix smtp-auth
unix_listener /var/spool/postfix/private/auth {
mode = 0666
user = postfix
group = postfix
}