> 1. NEVER EVER login from an email link.

I receive Google Doc links periodically via email; fortunately they're almost never important enough for me to actually log in and see what's behind them.

My point, though, is that there's no real alternative when someone sends you a doc link. Either you follow the link or you have to reach out to them and ask for some alternative distribution channel.

(Or, I suppose, leave yourself logged into the platform all the time, but I try to avoid being logged into Google.)

I don't know what to do about that situation in general.

> leave yourself logged into the platform all the time

Or only log in when you need to open a google link. Or better yet, use a multi-account container for google.

As for any of these cases, we do receive legitimate emails that require being logged in, Google or otherwise

The answer is simple: use your bookmarks/password manager/... to login yourself with a URL you control in another tab and come back to the email to click it

(and if it still asks for a login then, of course still don't do it)

Log into Google, then click the link. If you get prompted to log in again, don't.