Deferred message are events observed when the destination server is temporarily limiting the inbound mail. In such situations, the sender (this would be our mail server in this case) will attempt to send the deferred message for up to 72 hours until it delivers it. If the delivery is not completed within the mentioned time frame, the message will bounce, thus triggering the entry inside the "Track Delivery" feature in the cPanel.

You can associate this response with the busy signal older stationary phones used to transmit from time to time. Here are a few reasons why this could happen:

• The receiving server does not recognize the IP address that is sending the message and is linking it with spam. This could also mean that email spoofing is taking place.
• The receiving server ports are fully occupied, which means that it cannot accept messages at this point.
• The recipient's mailbox is full.
• The emails sent by the SMTP server have been marked as spam by users of the destination server. This act has associated your mail server's IP with spam but not to the point where it will immediately bounce your messages. In this 72 hour window, the incoming mail server will delay the inbound mail, waiting for users to mark messages from your server as relevant. In this case, it will complete the delivery. However, if users flag it as spam, the server will bounce it back.
• Since we use cPanel, deferred messages can trigger from the fact that you have sent a lot of emails in a short time (usually 1 hour). This consistency may reach the "Maximum percentage of failed or deferred messages a domain may send per hour" value,  thus putting the domain on a temporary inability to send emails. The "Maximum percentage of failed or deferred messages a domain may send per hour" count will keep getting refreshed each time you attempt a new email delivery, practically rendering you completely unable to send emails. This leads up perfectly to our last bullet point.
• An exploited Email, cPanel accounts, or web application can be the reason for the deferred messages. Typically, this is the reason for deferred emails 90% of the time in our experience. We recommend using strong, randomly generated passwords which you store on remote locations and copy-paste them in the passwords fields. Alternatively, you can use a password manager tool, such as LastPass for your passwords. To reduce the chance of your web applications getting hacked, make sure you keep them up to date, along with their plugins and themes.

There are exceptions to the above criteria, and if you are facing issues with deferred emails and none of the above recommendations are proving useful, please reach our technical support team by submitting a ticket from your Client Area.