That's up to the user to decide. For me trustworthy = something like Basecamp, Amazon, etc, not some random small app.
> trustworthy = [...] Amazon
Good point, because your example includes one of the few companies I don't trust at all.
Trust not to misuse.
Trust not to leak in a breach.
Realistically, my email address is something I trust Amazon with both of, because email isnt how they spam me, they are smart enough they can identify me without my email address, and I expect their security to be more hardened and battle tested.