News: Internet/Email in Small Business

Email Issues: Will the real email please stand up?

Authentication techniques require constant attention

by Keith R. Wheeler

2/15/2006

With the onslaught of unsolicited, junk email growing at a seemingly exponential rate, it would be logical to think that there is some way to slow it down. Well, there are lots of ways in place to slow it down. Unfortunately, they haven’t been very well coordinated. In fact, some of the mechanisms in place actually prevent valid and legitimate email from reaching their recipient. Sender authentication techniques require the email be sent with some type of password checking prior to being sent out into the broad internet space. This has prevented what’s called open relay sending. Spam emailers would look for an open relay to send messages without having to know the password authentication. Ultimately, some major internet service providers created a test to see if the email they were receiving was sent through an open relay. If it came through an open relay, it was then rejected. This forced email servers to close open relays in order for their clients’ email to not get blocked. Another method of email authentication which is in use is Reverse DNS Lookup. Email servers receiving a message would examine the IP address where the email originated. The server would perform a reverse DNS (Domain Name Service) lookup. The sender’s ISP has to be involved to set up the Reverse DNS since they manage the IP address used to send the email. The test then yields a name which can be matched to the sender’s email address’ domain name. If the name matches, or if the server can find that the sending domain also resolves to the same IP address as the Reverse DNS name, the email is accepted. If no match, the email is rejected. A recent addition to the authentication techniques is the use of Open Sender Policy Framework, OpenSPF. This approach works a little differently. For each domain name on the internet, there is zone file. The zone file includes information about where web requests and emails for the domain get routed. For OpenSPF to work, a record is added to the zone file which defines which email addresses and/or domain names are valid. When an incoming mail server applies OpenSPF, the SPF record is acquired and used to determine if the incoming mail is from an pre-defined source. All three of these methods, open relay checking, reverse DNS lookup, and OpenSPF try to reduce the amount of spam by requiring the sender to perform some type of authentication. There are other schemes in place which attempt to filter the content for the receiver. The result of all of this does reduce email at the expense of some legitimate senders who don’t have some part of their email system completely up to date – according to the latest attempt of the big ISP’s.