Trends The Slowest Mail Servers in the World By Ken Simpson | 3 minute read MailChannels periodically surveys about a million mail servers around the world to find out what MTA software they are running. This survey is called PingedIn, and I have written about it previously (see the Network World article by Michael Osterman). Recently, we enhanced PingedIn so that it keeps track of the amount of time it takes for the mail server we are connecting to to respond to each SMTP command. By analyzing these delays, we can make some very rough inferences about how heavily loaded a mail server might be relative to others in its class. For fun, I summarized the slowest mail servers, looking at just two of the response times we track: Banner Delay – this is the length of time between establishing a TCP connection with the mail server, and receiving the initial SMTP banner; and, HELO Delay – this is the length of time it takes to receive a response to the HELO command (HELO with no arguments, BTW). The banner delay does not necessarily indicate that the mail server is overloaded. Many service providers insert an intentional delay (called the “Greet Pause” by some), to hopefully deter spammers. Other providers use traffic shaping – MessageLabs is a good example – which slows down responses to all commands unless you are a trusted sender. If the HELO delay is large, it more probably indicates a slow or overtaxed mail server. While many providers seem to provide an intentional banner delay, far fewer choose to delay subsequent commands. So if the HELO response is slow, it probably means the mail server is overloaded. The following chart and table summarize the slowest overall mail servers and email services, based on the sum of their banner delay and HELO delay: (click on the chart for a larger version) The slowest entry is the Electric Mail Company (a division of j2 Global Communications), a service provider with a considerable base of mostly small business customers. I know that Electric Mail has always been a pioneer in using protocol-layer approaches to deter spam, so their long delays are likely intentional. Next up is DirectNIC, a cheap domain registrar. DirectNIC uses Sendmail, and I think it’s fair to guess that they have enabled the greet pause function to delay the banner, since their HELO delay is not too bad at only 1.2 seconds. At 5.33 seconds, MXPath’s HELO delay is also considerable. MXPath is a hosted email security service (by the looks of it, anyhow). Interesting entries: Frontbridge – this is Microsoft’s hosted email security service. At 3.2 seconds, their HELO response is 50% greater than average. The banner time is also high – are they using a greet pause, or is this indicative of performance issues? Symantec Norton Anti-Virus Gateway – Banner delay? Can anyone from Symantec comment? If we set aside the banner delay and examine only the HELO delay, we arrive at the following chart: The front-runner for HELO delay is, once again, Electric Mail. At 15.39 seconds, their HELO delay is more than seven times the average. Looks like an intentional greet pause. More surprising, in my opinion, is the appearance of Google and Yahoo in the top ten HELO delays. Google has a large and flexible number of email servers, as does Yahoo. Are their HELO delays the result of traffic shaping, or high load? What’s your email server delay? Why not call us and we’ll run a load test.