I've gotten as far as making the picture small (Preview, View, + or -) then get the message from Forum that no file is attached, that I haven't figured out yet.
Go to "share" and then "email". It let's you resize. You'll get lots of stuff about emailing you don't need so just keep closing those. Finally you'll end up with what you want.
If you have a Mac, drag photo out of iphoto onto the desktop. Click on photo on desktop preview will open photo, click on Tools at the top of screen and go down to adjust size.
I worked on it last night and was able to reduce the size. Got it down to about the size of a postage stamp, which must have been about the correct size because it wasn't rejected but got the message something to the effect that no file was attached. This 'puter talk would drive a preacher to drink. And I ain't no preacher.
You gave me some ideas that I'll work on. It was way past dark thirty and I went to bed, after I had a drink.
Alternatively, when you have the photo selected, choose File > Export. It gives you the option to rescale however you like, or to change formats for email, webpage, etc.