send-error-email.apex

/* Example for sending an email when there is an error on a JSON request */
private static void sendErrorEmail(String method, HttpResponse response, String requestJSON) {
    Messaging.SingleEmailMessage message = new Messaging.SingleEmailMessage();
    message.toAddresses = new String[] { 'me@example.org' };
    message.subject = 'Error in ' + method + ' : ' + response.getStatusCode() + ' - ' + response.getStatus();
    if (requestJSON == '' || requestJSON == null)
        message.plainTextBody = 'No body';
    else message.plainTextBody = requestJSON;
    Messaging.SingleEmailMessage[] messages =  new List<Messaging.SingleEmailMessage> {message};
    Messaging.SendEmailResult[] results = Messaging.sendEmail(messages);

    if (results[0].success) 
    {
        System.debug('The email was sent successfully.');
    } else 
    {
        System.debug('The email failed to send: ' + results[0].errors[0].message);
    }
}