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"We" tried this in the late 1990s. I remember writing an exim config to do this a couple of ways back in my ISP times: 1. "The recipient will not get this mess
by PaulRobinson 3mo ago
"We" tried this in the late 1990s. I remember writing an exim config to do this a couple of ways back in my ISP times:
1. "The recipient will not get this message until you authenticate yourself as a legitimate sender at this URL [...]" - resulted in people never getting mail from no-reply addresses they cared about (banks, e-com, etc.)
2. "This sender has sent you an email, with this subject and this first paragraph. Click here to whitelist, here to blacklist" - created a lot of churn on first setup that users didn't like as a UX
Baking it into the protocol - even now in SMTP and IMAP land - is doable, but would be resisted by email providers who, for example, make their money selling data to marketing agencies. Like, you know, Google, Microsoft, Yahoo...
I've seen other approaches proposed - even at IETF level - over the years, including digital postage stamps (sender pays to send email, your server gets paid, and may reject non-stamped/paying email), but it's the usual network effect: until it becomes widely supported it won't "stick". The stuff that has been adopted has basically been stuff that Google likes, period.
- baudehlo 3mo agoIt also misses one of the biggest fundamental problems with SMTP: Lack of per-recipient replies. Though you could potentially mandate a single recipient per request. We wrote a plugin to emulate that in Haraka, where you just 400 (temp fail) each subsequent recipient. The downside is some sources just plain don't retry.
- inigyou 3mo agoLMTP is a small modification of SMTP with a per-recipient response code - but I'm not sure what it's intended for. It isn't used on the internet. It's sometimes used as IPC within a mail server.
- baudehlo 3mo agoLMTP is for delivering to an IMAP (or JMAP) mailbox, generally. We also have a plugin for that. But it has certain flaws for exposing it to the internet (I just forget what they are right now).
- inigyou 3mo agoThere's no such thing as an IMAP mailbox. Mail receiving is split down the middle. Your SMTP server stores the email in a folder and your IMAP server provides access to that folder.
- baudehlo 3mo agoThat's not how things work at all. For context, I'm the author of Haraka, a popular open source SMTP server. SMTP servers don't necessarily store anything. They have two responsibilities: Receiving and delivering email. What they do with the emails they receive is up to the configuration.
- inigyou 3mo agoBaking any of these into the protocol will invalidate it. If there was a standard way to specify a URL to open to whitelist an address, spammers would just whitelist their addresses.