Just a suggestion as I have never needed to do it........
How about using a web hosting such as Skydrive which is a Microsoft product > upload the zip file to skydrive > copy the url and past it to you reply as a link.
Thanks for the various suggestions. Not sure how. Finally managed to upload a zip file with less in it. Both were well below the upload limit. Either way, these new options suggested above are duly noted for the future. Thanks!