When receiving an email from a major provider, such as Gmail, Outlook, or Yahoo, there is sometimes a delay in the message arriving in your inbox.
cPanel implements an automatic delay when new servers connect to your server to deliver mail; this is a protection to prevent spam.
In WHM, there is an option to bypass this delay for major email providers:
- Log into WHM
- Navigate to "Exim Configuration Manager"
- Enable 'Do not delay the SMTP connections for hosts in the Greylisting "Common Mail Providers" list'
Please see this article for a description of the setting mentioned above.
And see here for a related feature, Greylisting.