When you do the > image size, check the dots per inch (DPI) in the
dialog box
It will need to be 96 DPI best to send via email or load onto the
Internet.
800 pixels wide by 600pixels high will be around 150 kilobytes.
Congratulations, completely misleading and confusing.
Both DPI and print size are
completely irrelevant to emailing, to viewing images on screen at 100% or filling the screen, to internet, to putting on a webpage. They only have any significance in DTP and in printing, and even there these settings are often overriden.
In order to make something appear suitably big or small on (say) a website, it has to have a suitable number of pixels. This also reduces the file size to something smaller and more suitable for emailing.
The simplest and best way to resize an image down to 800x600 pixels, say, is to
ignore the resolution,
ignore the print size, put ticks in the "resample" box and in the "constrain proportions" box, then in the Pixel Dimensions boxes type in how many pixels wide you want the image to be. The height is set automatically to match.
Then use "Save As" and choose JPG as the file type. Quality setting 6 is "convenience" photo quality, 9 is plenty for most purposes (we're talking about a small email-friendly file here, not a high resolution wonder).
RP