SMTP Authentication Update
Opinion: It's about 2 and a half years since the standards bodies threw up their hands and left SMTP authentication to the industry. Implementation progress has been slow but positive. And there have been some surprises.They were heady days back in 2004 when the industry tried to reach consensus on a standard for SMTP authentication. The MARID (MTA Authentication Records In DNS) standards effort went down, partly in the flames of a political fight over patents with Microsoft, but the larger truth of the matter was that changes to heavily used standards like SMTP are bound to generate resistance from numerous sources, many of them with valid concerns. But changes can come slowly, one site at a time over a period of several years. And sometimes they can be made more effectively when pushed by a big, strategic company than a standards body. A little catchup on the terminology:
- SPF (Sender Policy Framework) is a standard for authenticating messages by checking special records stored in the DNS for the domain that the message claims to be from. But it only checks the message envelope (the MAIL FROM statement in SMTP) and thus misses quite a bit of SMTP fraud.
- SIDF (Sender ID Framework) is Microsofts approach to authenticating the entire message. The heart of it is the determination of a PRA (Purportedly Responsible Address) for the message and checking the domain of that address to see if the messagess sending agent is authorized. SIDF incorporates SPF as a first-stage test and stores further records in DNS in XML format.
- DKIM (DomainKeys Identified Mail) is the merger of two similar standards from Yahoo and Cisco. It too uses DNS-based records to authenticate a messages sender as authorized for the domain of purported sender but uses a public key cryptography scheme for the authentication, removing the need to track actual IP addresses of servers.
Often the best way to thwart spamming and phishing is to take down the domain names involved in it, but this is a hard thing to do under current rules. Click here to read more.