Actual vs Large photos in mail.

I use Lightroom which lets me export a large image to a large range of physical sizes and file sizes (amount of compression used for a jpg image). I would think most photo editing software will have similar features. As I remember in iPhoto you select an image and Share it via an email. iPhoto lets you decide the size of the image to be put in the email.

You can also Export from iPhoto and choose your own custom size, plus you can resize using Preview.