postgrey whitelisting outlook.com

Greylisting is a way of reducing the amount of incoming spam and virus emails, in addition to other counter measures. Postgrey is a good choice if you are running postfix.

However, to be able to recieve emails from senders using outlook.com you need to whitelist it. This is because outlook.com is using a different host on each try to deliver the mail, causing delays up to hours, days or the mail not being delivered at all within time limits.

Create/edit the file /etc/postgrey/whitelist_clients.local and add:

# outlook.com
/^.*\.outbound\.protection\.outlook\.com$/
/^.*\.prod\.outlook\.com$/

Then execute:

service postgrey reload

Edit December 2021: The rule is changed from /^mail-.*\.outbound\.protection\.outlook\.com$/ to /^.*\.outbound\.protection\.outlook\.com$/ as Microsoft has changed their server naming standard.