I asked DB support about the sharing issue with multiple email addresses, and here is their response:
Dropbox does not know, that one is your old and one is your new email address. Dropbox knows, that you have a Dropbox account with the email address <old> (because you are logged in or connected on the device), although you received and try access through another one.
When you try to access a shared folder with another email address than the invited one, you send a request to the sender and he has allow to it. Otherwise you can not access the shared folder.
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If I change the email address associated with my account, what will change? I've seen this post, which says that nothing will except for my login info and my notification email address. However, what about folders that have been shared with me (under my old email address) and folders I've shared with other (under my old email address)?
I'm a little confused about how email addresses are managed, since if I receive a folder invite to <new email address>, and click (in gmail) the link that says "open folder", I get the following message: "<new email> was given access, but you’re signed in as <old email> ." (Note that both emails are forwarded to my <new email> gmail account.) But then I'm allowed to accept the share. So how does Dropbox know that <new email> and <old email> are both mine? Or does it not care, reasoning that if I'm signed in to my email as <new email>, and into DB as <old email> and received an invite to <new email>, I've sufficiently verified my identity? (That doesn't seem particularly secure, since it relies on my email not getting hacked.)
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