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.