Cutting off your nose

November 18th, 2002

I’ve been trying to send email to a certain company this weekend but I always get the response:

smtp;550 5.0.0 Use your ISP’s SMTP server

I’m told that it’s because I don’t use my ISP’s SMTP server for outbound messages. Because this company’s ISP has decided that this could be a spammer tactic, they have decided to reject all mail from people who don’t send it through their ISP’s SMTP server. “Sorry, no Honda Civics on this road, sir, some people use them as getaway cars, don’t you know.”

Here are a few reasons why you might not send mail through your ISP’s SMTP server:

  • You use a non-windows system that uses the standard method of delivering mail via a local SMTP server.
  • You have an ISP whose SMTP server only allows outbound mail from addresses in its own domain
  • You have an ISP who requires POP access before allowing SMTP but you don’t care to use their POP mail
  • You don’t trust your ISP’s SMTP server’s reliability
  • You don’t trust your ISP’s DNS to reliably provide you the SMTP server address (you’re probably getting the idea that I have trust issues with my ISP)
  • You use a laptop at home, at work, dialup, elsewhere, and you don’t want to have to change the SMTP server every time you send a message

SMTP is designed to work this way. Breaking SMTP won’t fix the spam problem. Rejecting mail that’s sent in this perfectly reasonable way will just cause reasonable people to stop trying to send you mail.

6 comments to “Cutting off your nose”

  1. So are you saying this company would not allow me to use the SMTP server at my webhoster (which I want to use, after all that’s where the mail for my domain goes from/to…) instead of my ISP (which whole email service is useless)?
    This doesn’t make sense to me.

  2. Dunno exactly. I guess if you used your webhoster’s SMTP server, the IP addr of the smtp server would be in the webhoster’s address space and would likely be their main smtp server, so they’d allow mail to come to them from there.

    I take it they do a reverse lookup and find out that I’m a Rogers Cable IP address, but not the official SMTP box at Rogers.

    Being that there isn’t really any way to tell what the official SMTP server is for an ISP, I can only assume that they only do this for a certain list of ISPs. Being that it’s a Canadian company that is doing it, it’s not surprising that Rogers cable subscribers are on their hitlist.

    What they end up blocking, then, is only people who make SMTP connections from within an ISP’s customer space. Not just relaying, mind you, but direct connections. If I telnet to their port 25 as though I were going to send a message directly to their machine, I get the same message.

  3. Fascinating stuff Brent. And indeed very interesting. This is the first step in the long path down email starting to break badly which I will predict will happen.

    There are only 2 real solutions:

    1. From a email user perspective, use your address book as a white list to accept emails only from certain users and filter everything else as spam. Fish out false positives on an as needed basis.

    2. Start charging for outbound email.

    Your ISP may have started to aim towards #2 but missed the point. They are basically covering their butts on the email receiving side due to the fact that people are very careless about leaving SMTP servers in relay mode. I am not surprised this is happening and it will get worse trust me.

    An interesting technologies to check out:

    TMDA http://sourceforge.net/projects/tmda

    This basically adds a reasonable whitelist capability. I am convinced that in the next 5 years all email clients will support only receiving email from a whitelist addressbook with an easy way to fish out false positives.

  4. A few interesting articles on the whitelisting topic


    And a slashdot post


  5. Here are some articles I used to write for ClickZ… Read em and weep. Email is going to hell in a handbasket. “Danger Will Robinson, Danger”


    Love to hear your feedback on some of the musings.

  6. I need to find a national isp that does not block smtp mail from my website. Any out there?