I just looked through the archives, and Dave seems to be right; I never
did fully explain how I think Docomo e-mail (and mobile e-mail in general)
should work. So here are my thoughts on the matter.
All incoming e-mail should be coming to my mail server. This gives me an
address at my own domain (in this case, keitai@cynic.net) and allows me
to keep a copy in my regular mailbox and do some spam filtering. (The
former is handy because I can reply from a real keyboard if I happen
to be near one, and I also have a copy that hasn't had the attachments,
if any, trimmed. The need for the latter is fairly obvious.)
Once the incoming e-mail is relayed through my mail server, I can
block all e-mail to the phone that doesn't come from there. Docomo's
blocking is based on the envelope sender (the address in the SMTP "MAIL
FROM:" command), so all I need to do is pick an appropriately unlikely
envelope sender (jkd743orjetdeoemehyd7694mrl@cynic.net, or something
similar) for the mail I relay, and block all e-mail that's not from that
sender. Conveniently, what's displayed in the "From" field on the phone
is the address in the "From:" line in the message itself (the "message
sender"),so I leave that set at whatever it was before, and the e-mail
looks identical when it reaches the phone.
It is possible for spammers to attempt to work out the envelope sender
I'm using and use that information to send spam directly to the phone
anyway, but it's not likely to be worth the trouble to them to forge an
envelope sender just for me even if they know what it is.
The only problem now is outgoing mail, which still has my @docomo.ne.jp
address in the From: line. I get around this, currently, by sending
mail back to a cynic.net address with the real recipient in the Subject
header. A program on my mail server processes the mail to give it a new
from line, subject (「カートから」, in this case) and makes the old
subject line the new To: line and envelope recipient, then forwarding it
on to that address. The only hitch here is that the maximum length of a
recipient e-mail address on my phone is 50 bytes, but the maximum length
of a subject is only 30 bytes. I've already run into this limitation,
so I'm going to have to change my system so that the first line of the
message is the desired recipient, I suppose.
From a user interface point of view, this process isn't as bad as you
might think, at least on my P209i. When I want to reply to a message,
I first copy the sender before I reply, then I paste the sender in the
subject field and recall my special cynic.net address from my phone
book to the recipient field. (I start its reading with a space, so just
hitting the down button in the recall-by-name screen brings it up.)
Much better, of course, would be if I could convince Docomo to put in
my cynic.net address on all e-mail I send, but I don't anticipate this
happening any time soon.
Of course, at this point I'm not sure all this work is really necessary
just to prevent spam, if you're not using an 090nnnnnnnn@docomo.ne.jp or
otherwise excessively simple address. But I like getting my mobile e-mail
copied to my regular mailbox, and the potential to switch phone vendors
without changing my address. As well, if the spammers ever grab a brain,
they'll have no problem discovering a lot of the non-number addresses as
well. (You can sit there all day giving SMTP "RCPT TO:" commands to the
Docomo SMTP servers, with it conveniently telling you for each one whether
or not the address exists. It would be not even a day's work to write a
perl script that would check all combinations of 1-4 Japanese syllables,
and that would run through them all in a couple of weeks or so.)
cjs
--
Curt Sampson <cjs@cynic.net> +81 3 5778 0123 de gustibus, aut bene aut nihil
Basically, a tool is an object that enables you to take advantage of the laws
of physics and mechanics in such a way that you can seriously injure yourself.
--Dave Barry
[ Did you check the archives? http://www.appelsiini.net/keitai-l/ ]
Received on Wed Jul 25 05:08:46 2001