@digfish Not always legally and not always even technically as publishers have sued ResearchGate for hosting that material and ResearchGate has developed tech to check the copyright when you upload it. https://cen.acs.org/policy/publishing/Science-publishers-settle-lawsuits-ResearchGate/101/web/2023/09
Posting on a university repository is usually allowed, with various annoying limits; emailing when requested is always allowed, because it's inherently limited, and also they can't stop you and would look bad if they tried.
@zeborah @RustyBertrand does academia.edu also faced attempts of being sued by publishers? Who owns the copyright of scientific papers, after all?