vi /etc/postfix/postgrey_whitelist_clients

# Do NOT greylist hotmail.com MX servers (see dig in mx hotmail.com)
/^mx[1-4]\.hotmail\.com$/

# Do NOT greylist ANY host from hotmail.com or outlook.com

#hotmail
/^.*\.hotmail\.com$/
#outlook
/^.*\.outlook\.com$/

killall postgrey
service start postgrey

Log:

postgrey[30881]: action=pass, reason=client whitelist, client_name=bay004-omc4s14.hotmail.com, client_address=65.54.190.216, sender=

You also can whitelist *.outbound.protection.outlook.com and etc