On Mon, Feb 22, 2010 at 10:30 AM, Jeff Kell <jeff-kell@utc.edu> wrote:
There's no way to do this without some underlying forwarding... and
Forwarding SMTP traffic consumes major bandwidth resources (potentially), as the number of 'ports' eventually increases, and seems like a juicy target for many different types of potential abuses. There are major technical hurdles that should be considered, otherwise ISPs probably wouldn't care much to provide mailboxes, and instead: might simply recommend an overseas service (not subject to the port rules) for people who want e-mail. Or include "purchase of a domain name" in the price of getting e-mail service, it's just another "tax" required due to government regulations, ISP/telephone/cable subscribers are already used to those types of fees. When the end user purchases their own domain, it's up to them to transfer their own domain name and deal with all the technical issues that entails. Issues like: spam against forwarded addresses (impossible to reliably implement SPF and other sending MTA based protections). Possibility of the "porting mail server" being blacklisted (interfering with forwarding), having, sketchy connectivity, or other persistent issues, or low message size limits "No more than a 500mb attachment can be forwarded", that might have been the reason the user switched e-mail providers in the first place, so they could receive 30gb HD-DVD ISOs their friends were e-mailing them..... Resolving the destination address is what DNS is for, not what SMTP routing is for. Perhaps there is... Give every e-mail user a subdomain as in examplemailbox@examplemailbox.example.com To "port" an e-mail address, the receiving ISP then provides a domain name server for the donor ISP to publish as in... mailbox.example.com IN NS theirdns1.example2.com Use "IN NS" subdelegation to the user's new ISP. This requires the ISP to "plan for portability", by designating a subdomain for each user, and having DNS software that can handle (potentially) hundreds of thousands of permanent mailbox records. For authentication, to request a change, make it be proven that the request is coming from a legitimate authority of the host the "IN NS" record points to. Or else rewrite the SMTP specification to change how the SMTP server is selected for every single e-mail transaction (assuming the internet community actually thinks this is worthwhile).... Instead of merely performing a lookup of MX against just the host label (where MX exists), bring in Mailbox binding As in bring back RFC 883 MAILB: QNAME=mailbox@mx.example.com QTYPE=MAILB after a successful response from a QTYPE=MX query. If NXDOMAIN is returned from MAILB then proceed to contact the MX. But if MR responses arereceived from the MAILB query, then the sending MTA should switch to the recipient destination as directed. And repeat the MX and MAILB lookup process with the new destination... But the presence of a MAILB record must not imply that the e-mail address likely exists. The absence must not imply the e-mail address likely doesn't exist, either.... Otherwise spammers would be very happy. ISPs must wildcard MAILBs or have some very robust abuse-protections in DNS itself, or end-users would never want to use MAILB-based porting. -- -J