We have a contact form on our website. When a user completes the contact form an email is sent to the user plus a copy to a ZohoMail user (sent via standard WordPress functionality). The user gets their email immediately but for some reason the cc. emails to ZohoMail users are being delayed by exactly 20 minutes. I don't understand why is Zoho delaying the receipt of this email? 

Normal emails from customers to ZohoMail users are received immediately. Seems to be only emails sent via WordPress. Can you please advise why and how we can get the message immediately.