Instructions for my suggestion above:
To create a multi-part ZIP:
- Download lastest evaluation version
here and install with default options
- Right-click the file to zip and choose "Winzip/Add to zip file..."
- Click "use evaulation version"
- Look for "Split Zip file" and click where it says "Don't Split"
- In the drop-down list, choose desired size for each piece, e.g. 3Mb
- Click "Add" button in top-right
- Done! Email each piece separately