the problem:
myhostname postfix/smtpd[26105]: fatal: open database /etc/postfix/sender_whitelist.db: Bad file descriptor
myhostname postfix/master[25978]: warning: process /usr/libexec/postfix/smtpd pid 26105 exit status 1
myhostname postfix/master[25978]: warning: /usr/libexec/postfix/smtpd: bad command startup -- throttling

solve this problem:

# vim /etc/postfix/main.cf

remove this config "check_sender_access hash:/etc/postfix/sender_whitelist" and then restart postfix service.