Invoking a Lambda Function when Email is Received

I believe you would have to use SES to recieve emails in turn you could then trigger a Lambda function.

However, yes you can use eventbridge CRON schedule to trigger Lambda/StepFunction https://docs.aws.amazon.com/eventbridge/latest/userguide/eb-run-lambda-schedule.html

Another option is to leverage workmail: https://docs.aws.amazon.com/workmail/latest/adminguide/lambda.html