What is Relaying?
When you send a message to an SMTP server (such as smtp.myaccess.coop), and that message is addressed to an account that isn't on that server (such as email@example.com), then the SMTP server has to pass it on to the addressee's mail server. This action of passing the message on to the destination mail server is called relaying the message.
Then What Is An Open Relay?
Most mail servers are set up to serve a particular organization's or individual's network. Normally, the mail server will be configured to relay mail only for users on that organization's network. Sometimes, however, a mail server is misconfigured, and allows users anywhere on the Internet to relay mail through it. A mail server that is misconfigured in this way is called an 'open relay'.
Why Is This A Problem?
If your mail server is an open relay, spammers can send their junk to your mail server and your server will automatically relay it to thousands or millions of recipients all over the world.The obvious result of this is that the spammers have effectively stolen resources from your mail server. By relaying such large quantities of mail through it, they will likely be slowing it down and causing delays for your own legitimate users. They are also using huge amounts of your bandwidth, slowing down your Internet connection, and possibly causing you to be charged for the high bandwidth usage.Having your mail server appear to be the source of spam also damages your reputation in the Internet at large. You might even get blacklisted. This means that if your mail server is misconfigured as an open relay, you will soon no longer be able to send even legitimate email to many people.
Do Open Relays Cause Other Problems For Internet Service Providers (ISP)?
Yes, they certainly do. The issue of reputation in the Internet at large is a lot more significant for a large ISP. If an ISP starts to be known for harbouring spammers or open relays, other ISPs and networks around the world begin to take actions like blocking all traffic from that ISP. This is a serious concern, and one that Access Communications does not take lightly. It is for this reason that we actively pursue all spammers and open relay complaints against our customers.Additionally, some customer mail servers are configured to relay all email to the ISP's mail server. The ISP's mail server then sees all the email as coming from the customer's mail server, and accepts it for relaying. The problem with this is that if the customer's mail server is an open relay, then it will be accepting spammers' email from all over the Internet, and passing it on to the ISP's mail server, which will then relay it to the destination. This is a serious problem because, to the outside world, it will then look like the ISP's mail server is an open relay.
What Should Mail Server Administrators Do About This?
Mail server administrators whose mail servers have been misconfigured as open relays should work to correct the problem immediately. They should configure their mail servers to allow relaying only for messages sent from computers on their local network, as recommended in the Internet Engineering Task Force (IETF) RFC 2505.We have compiled the following list of links to documentation on correctly configuring some popular mail server products against open relay problems. Also, mail server administrators can test their mail servers for open relay problems via Abuse.net's relay tester. Please note that all of the below links are hosted outside of Access Communications, and are provided for mail administrators' convenience only. The information provided at these links is not supported by Access Communications.
Is There Anything Else Administrators Should Do?
If a mail server has been an open relay for very long, it will likely be listed in several databases of open relays, such as the ORDB. After fixing the configuration problem to disallow relaying to non-local computers, the server administrator will have to request that the organizations operating these databases retest the mail server, and remove it from their database. Most such organizations will have prominent links on their website to submit an IP address for removal from their database.Until the mail server has been removed from these databases, many other mail servers (including the Access Communications mail server) may refuse to accept mail from it.