Disable Greylisting
Disabling Greylisting helps to receive emails without any delay.
touch /etc/postgrey/whitelist_clients.local
nano /etc/postgrey/whitelist_clients.local
Add contents:
# Don't greylist any domain.
/.*/
Save and Exit, then:
service postgrey restart
service postfix restart
Source: https://discourse.mailinabox.email/t/disable-greylisting-modify-whitelist/137/2