Retroemailsendmailsysadmindebugging
A Botched Server Patch Stopped a University's Email at About 500 Miles, and the Speed of Light Set the Limit
Trey Harris's account of the 500-mile email: a SunOS upgrade quietly downgraded Sendmail, zeroed its connect timeout, and turned three milliseconds of light travel into a map radius.
Harris opens with a warning: “Here’s a problem that sounded impossible.” At the time, he writes, “I was working in a job running the campus email system some years ago.” Then the chairman of the statistics department called with a complaint: “We can’t send mail more than 500 miles.”
Harris assumed he was being put on. The chairman explained the delay in reporting it: “Well, we hadn’t collected enough data to be sure of what was going on until just now.” This was a statistics department, and a colleague had done the work. “She’s produced a map showing the radius within which we can send email to be slightly more than 500 miles,” as Harris retells it.
So he tested it, “scarcely believing that I was playing along.” Mail to nearby places went through. “But then I tried to send an email to Memphis (600 miles). It failed.” Boston failed. Providence, at 580 miles, failed.
The clue came when Harris asked what had changed. “Well, the consultant came in and patched our server and rebooted it.” The consultant had “apparently upgraded the version of SunOS, and in so doing downgraded Sendmail.” Worse, “the upgrade helpfully left the sendmail.cf alone, even though it was now the wrong version.”
The story has circulated for decades as a sysadmin legend, and Harris’s own post is the only account of it. He never names the university, so this piece doesn’t either. The mirror kept at MIT carries the same text.
The open question it leaves for anyone running servers today is how many stacks still treat an unknown setting as a default rather than an error. A config file that outlives its software version is still an ordinary thing to find after an upgrade.