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> but when I use Mail.app to send an email, I am the one doing the emailing, not the Google SMTP server acting as a mail transfer agent (MTA) You seem to be co

by sedachv 10y ago

> but when I use Mail.app to send an email, I am the one doing the emailing, not the Google SMTP server acting as a mail transfer agent (MTA) You seem to be confusing the MSA (https://en.wikipedia.org/wiki/Mail_submission_agent https://en.wikipedia.org/wiki/Mail_submission_agent) and the MTA. If today your MUA (Mail.app) tried to connect to the destination mail host via SMTP directly it would get rejected. Some early MUAs did actually do that, but today almost all email gets relayed via an MSA and one or more MTAs.

extra88 10y ago
As the Wikipedia article says, "Many MTAs perform the function of an MSA as well." I was looking at the article about MTAs [0], in which the diagram does not bother showing the sending MUA connecting to a distinct MSA. My MUA would not be rejected by the destination host if the recipient uses the same host as me. [0] https://en.wikipedia.org/wiki/Message_transfer_agent https://en.wikipedia.org/wiki/Message_transfer_agent
- sedachv 10y ago
  > My MUA would not be rejected by the destination host if the recipient uses the same host as me. Your MUA would be rejected if it acted as an MTA and connected on port 25 without authenticating. "Using the same host as me" is the case because the mail server knows that it is "your host" because your MUA is connecting to your email server's MSA using SMTP AUTH on port 587 or 465.
  - extra88 10y ago
    Well now you're moving goalposts, qualifying connections by port and authentication. I'm sure what you write is true of most ISPs and major email service providers but there are still SMTP servers in the world that don't require all MUAs to make authenticated connections; there's at least one at my university.
    - loup-vaillant 10y ago
      They don't require authentication because they only accept relay requests from within the university network. Otherwise they'd be an open relay, and those tend to relay spam as soon as spammer spot them, then they get blacklisted by most spam filters. In any case, this doesn't affect my main point: by using those, you still don't send your email yourself. In my book, "sending your own email" means you operate your own mail server, without using any third party relay (not Gmail's, not your ISP's). I'm personally halfway there: I have root access to a virtual machine on the cloud (gandi.net), and configured it to relay my email for me. Next step would be to have physical control, but I kinda abandoned that idea when I learned that residential IPs are blacklisted (Hotmail even made it an explicit policy, it won't even appear in the recipient's spam folder).
      - extra88 10y ago
        > In my book, "sending your own email" means you operate your own mail server Virtually no one else reads that book. To everyone else, the user operating the MUA is sending their own email.
        sedachv 10y ago
        If you use Gmail via webmail at https://mail.google.com https://mail.google.com or have a MUA like smtpmail.el in Emacs connect to smtp.gmail.com, Gmail is still sending your mail.
        cwyers 10y ago
        This is like saying that unless you own your own post office, you're not sending your mail, the US Postal Service is. Nobody talks like that.
        loup-vaillant 10y ago
        We trust the postal office to act as a reliable dumb pipe. Most email services are far from that: they filter inbound email in a way you have little control of. They spy inbound and outbound mail, and use that information to send you ads. Also, they control your right to send and receive email: if your account is terminated for some reason (they reserve the right to, blah, blah), you cannot move to a new provider, or redirect inbound mail or nothing: they own your email address. Still think your send your own email? Fool.
cdh 10y ago
Perhaps I am misunderstanding you, but while it is certainly uncommon, it is absolutely possible to directly deliver mail to a recipient's SMTP server. In many cases, this can be done without any authentication whatsoever. I run my own mail server. When I send an email via the web interface, would you not agree the MUA is attempting to directly connect to the destination host? Depending on different factors, it may be classified as spam by the recipient, but from a reputable IP address it shouldn’t normally be rejected outright. Of course there are other factors like SPF, greylisting, etc... but email can be directly delivered.
- eikenberry 10y ago
  If you send from non-SPF listed IPs you will get rejected in many places and most likely marked as spam in those you don't. SPF particularly and DKIM and other anti-spam measure are in wide spread use and enforced by the receiving SMTP server either directly or via spam scoring system rules.

by sedachv 10y ago

extra88 10y ago

As the Wikipedia article says, "Many MTAs perform the function of an MSA as well." I was looking at the article about MTAs [0], in which the diagram does not bother showing the sending MUA connecting to a distinct MSA. My MUA would not be rejected by the destination host if the recipient uses the same host as me. [0] https://en.wikipedia.org/wiki/Message_transfer_agent https://en.wikipedia.org/wiki/Message_transfer_agent

sedachv 10y ago
> My MUA would not be rejected by the destination host if the recipient uses the same host as me. Your MUA would be rejected if it acted as an MTA and connected on port 25 without authenticating. "Using the same host as me" is the case because the mail server knows that it is "your host" because your MUA is connecting to your email server's MSA using SMTP AUTH on port 587 or 465.
- extra88 10y ago
  Well now you're moving goalposts, qualifying connections by port and authentication. I'm sure what you write is true of most ISPs and major email service providers but there are still SMTP servers in the world that don't require all MUAs to make authenticated connections; there's at least one at my university.
  - loup-vaillant 10y ago
    They don't require authentication because they only accept relay requests from within the university network. Otherwise they'd be an open relay, and those tend to relay spam as soon as spammer spot them, then they get blacklisted by most spam filters. In any case, this doesn't affect my main point: by using those, you still don't send your email yourself. In my book, "sending your own email" means you operate your own mail server, without using any third party relay (not Gmail's, not your ISP's). I'm personally halfway there: I have root access to a virtual machine on the cloud (gandi.net), and configured it to relay my email for me. Next step would be to have physical control, but I kinda abandoned that idea when I learned that residential IPs are blacklisted (Hotmail even made it an explicit policy, it won't even appear in the recipient's spam folder).
    - extra88 10y ago
      > In my book, "sending your own email" means you operate your own mail server Virtually no one else reads that book. To everyone else, the user operating the MUA is sending their own email.
      - sedachv 10y ago
        If you use Gmail via webmail at https://mail.google.com https://mail.google.com or have a MUA like smtpmail.el in Emacs connect to smtp.gmail.com, Gmail is still sending your mail.
        cwyers 10y ago
        This is like saying that unless you own your own post office, you're not sending your mail, the US Postal Service is. Nobody talks like that.
        loup-vaillant 10y ago
        We trust the postal office to act as a reliable dumb pipe. Most email services are far from that: they filter inbound email in a way you have little control of. They spy inbound and outbound mail, and use that information to send you ads. Also, they control your right to send and receive email: if your account is terminated for some reason (they reserve the right to, blah, blah), you cannot move to a new provider, or redirect inbound mail or nothing: they own your email address. Still think your send your own email? Fool.

cdh 10y ago

Perhaps I am misunderstanding you, but while it is certainly uncommon, it is absolutely possible to directly deliver mail to a recipient's SMTP server. In many cases, this can be done without any authentication whatsoever. I run my own mail server. When I send an email via the web interface, would you not agree the MUA is attempting to directly connect to the destination host? Depending on different factors, it may be classified as spam by the recipient, but from a reputable IP address it shouldn’t normally be rejected outright. Of course there are other factors like SPF, greylisting, etc... but email can be directly delivered.

eikenberry 10y ago
If you send from non-SPF listed IPs you will get rejected in many places and most likely marked as spam in those you don't. SPF particularly and DKIM and other anti-spam measure are in wide spread use and enforced by the receiving SMTP server either directly or via spam scoring system rules.