Laravel email validate issue and stop entire application

I have faced an issue with my Laravel application. I am going to place an order then showing an error message like the attached image below. Please anyone can help me to solve this issue. I don't understand wherefrom come up this issue.

Also please give file location for easier.

Screenshot.

    private function assertValidAddress($address)
{
    if (!$this->emailValidator->isValid($address, new RFCValidation())) {
        throw new Swift_RfcComplianceException(
            'Address in mailbox given ['.$address.'] does not comply with RFC 2822, 3.6.2.'
        );
    }
}

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