It's now to the point where the code for the "sending the first message" feature is looking trivial. For me, anyway, though, big challenges remain in user interface -- and mainly in training. I believe the number one risk is that adding this feature will further obscure the biggest advantage that sg has -- auto-create.
I've been thinking about it for awhile, and here's where I am now:
First -- we won't provide a form for sending a message. Instead, we'll provide an email address to send to. The user can click on a mailto: link or copy/paste into the MUA, and from there it'll work just like a reply does now.
What I'm thinking we should do is add a form that asks for:
a) a word
b) a count
c) a domain (eg, spamgourmet.com, xoxy.net, etc.)
e) the 3d party recipient address
Given this info, the UI will
1) a) create a new address record (and its corresponding private key) if the there's no existing address for the word,
or
1) b) refill an existing address up to the supplied count if it does exist -- also changing the domain to the specified domain if necessary.
and
2) use the private key from the new or exisiting address, along with the 3d party recipient address to generate a masking reply address the same way that the mail handler does now.
That address will then be presented to the user as a mailto: as described above. When the user uses it, it'll be handled like a reply is now, so no changes to the mail handler will be necessary. We also avoid the apparently undesirable situation of having email originate at the sg server.