But using internet protocols, the only way you'd have a corrupt file is if the download were incomplete; this could happen if your browser or download-manager is a bit dumb about deciding when the transfer has finished. Then you end up with a short file: the data you have is intact, but you don't have all of it.

In Outlook 2010 and later versions, the maximum size for a .pst file is 50 GB. The default maximum size for a Unicode .pst or .ost file is approximately 25 GB. The following Microsoft Knowledge Base article describes how to increase the maximum size of a .pst or .ost file:

File: Slow.Damage.zip ...