Solution
You will need to check your email account free space available, in the event that the email is bigger than the available email space of your email account, the email will be kept on our servers's mail queue�and it will attempt to resend to your account every hour, users are encouraged to check their email accounts to prevent unnecessary email delivery failure.
Do note that your email space is accounted for under the webspace of your hosting account, do note that in the event your hosting account is full, all mails will not be deliverable to your email account.