Have you tried changing your default mail app to Safari? It will still try to mail the page but you'll at least stay within Safari. That's the best solution I could find. https://apple.stackexchange.com/questions/261881/set-default...

Also found you on stackexchange while looking for an answer https://apple.stackexchange.com/questions/108060/how-to-prev...

Use https://github.com/Lord-Kamina/SwiftDefaultApps to changing your default mail app to Safari.

Agreed, not quite perfect but at least it doesn't open Mail.

thank you! I've been looking for a solution for this for YEARS.