SMTP is currently a push protocol and is initiated by the the
sender, no controlling that fact.
But it is possible to overcome the relay problems, IP spoofing and
domain impersonation etc,
by making the servers pull the mails.
US6192407
Ah, right, the famous Tumbleweed patent. Here's a better link
with a readable version.
http://www.google.com/patents?vid=USPAT6192407
This patent covers the idea of putting a message on a web server and
sending the recipient a URL to retrieve the message. Tumbleweed
enforces it very aggressively. See the list of suits in their
Wikipedia page.
Were it not for the patent, I expect we'd have a lot of institutions
setting up per-user password protected RSS or Atom feeds with
statements and other messages, and sending you mail telling you to
check your feed when there's something new.
R's,
John
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