If you host with GoDaddy, they have settings to change maximum allowed file size and Post, you can find tutorials/instructions to find it. But first, you need to make sure that .ppt files are transferred. You can create any file (a .txt file with something it it) or take an existing small file, rename it to .ppt and try to send.

Please copy-paste here what you currently have in Properties->Authorized extensions for the second File element, the entire value.