The simplest way to send a bunch of images is via email, you can upload your images to your email provider like gmail, outlook, fastmail etc. Most people have at least one email address and sending files like images to people via email is pretty common.
If your image files are relatively large, you can also consider using online file storage providers like Dropbox, Google Drive and Microsoft OneDrive, they're pretty solid and your files are safe with them. But if your client is not familiar with those options, that may bring some extra overhead for them to find out how to use these online file storage applications.
Another option is to use DpiApp, DpiApp is designed to aid designers to share designs, photos, illustrations with other people easily. You can upload your images to a DpiApp gallery, then share the link of this gallery to your client. Your client can then view these images from a phone or desktop web browser, without installing anything extra on their side. You can also set a passcode to secure your DpiApp gallery from being accessed by unwanted people.