Email Greylisting is a very effective anti-spam technique that involves temporarily block of certain unknown senders. This may cause you to receive some emails with some delay , so if the delay is not acceptable you may disable the greylisting on your domains.
To manage this feature, you must first access to the Hosting Panel.
In the email section, you will find the Greylist icon, click on it.
Here you will see you hosting panel domain list, with an On/Off switch. You can enable or disable Greylisting for each individual domain, just clicking on the switch.