The evaluations must be delivered to their recipients for a functioning system, but these need not necessarily be in a very timely fashion, since donations/offers of help are still helpful even if they take a while to arrive. The TO field of the evaluation is a URI (an identifier) which, in general, cannot be relied upon to act as a URL (a locator), so transport is non-trivial. However, some URI schemes also function as URLs.
Where the recipient of an evaluation is an email address, using ordinary EMail is the natural method of transport, so transport for mailto: evaluations is simple.
Http(s):// and others
The URL of someone's Facebook profile or their website is enough to identify them, but this does not equate to knowing their email address.