如果您在使用AWS Cognito时遇到在创建用户时有时无法发送电子邮件的问题，可以考虑使用以下代码示例：

1. 在AWS Cognito后台设置邮件配置：

{
    "cognito": {
        "userPoolId": "USER_POOL_ID",
        "clientId": "CLIENT_ID",
        "region": "REGION"
    },
    "ses": {
        "region": "REGION",
        "receiptRuleSetName": "SES_RECEIPT_RULE_SET_NAME"
    }
}

2. 完成用户的创建之后，调用AWS SES发送电子邮件：

const AWS = require('aws-sdk');

exports.handler = async (event, context, callback) => {
    const ses = new AWS.SES({
        region: process.env.COGNITO_REGION
    });

    const userData = event.request.userAttributes;
    const emailParams = {
        Destination: {
            ToAddresses: [
                userData.email
            ]
        },
        Message: {
            Body: {
                Html: {
                    Charset: "UTF-8",
                    Data: "
Welcome to my app!
You can now login with your email address and password.
"
                }
            },
            Subject: {
                Charset: "UTF-8",
                Data: "Welcome to my app!"
            }
        },
        Source: "myapp@example.com"
    };

    try {
        await ses.sendEmail(emailParams);
        console.log("Email sent successfully to " + userData.email);
        callback(null, event);
    } catch (err) {
        console.log("Error sending email: " + err);
        callback(err);
    }
};

通过上述方式发送电子邮件，即使AWS Cognito管理创建用户时有时无法发送电子邮件，也能保证用户接收到邮件。