Which version of Web Gateway? 6.8.7 or 7.x?
You can block access to those sites by setting the user's policy to block either the site or webmail category.
To block the uploads but still allow them to login and read e-mail, you would need to do SSL scanning to break into the encryption, and then find something in the traffic that you can use to recoginze an upload to block it.
I know those are generic answers because I don't know which version of Web Gateway you are using. We can point you in the right direction, but if you want to block the uploads, you are going to need to do connection tracing and/or packet captures to try and find something to recognize a file upload.
it's Web Gateway 7.x, update to new version!
i also facing the issue. webmail is allow to read but not attachment can be upload. may i know how to do it. i using MWG 7.1