I was working in a job running the campus email system some years ago when I got a call from the chairman of the statistics department.

"We're having a problem sending email out of the department."

"What's the problem?" I asked.

"We can't send mail more than 500 miles," the chairman explained.

I choked on my latte. "Come again?"

"We can't send mail farther than 500 miles from here," he repeated. "A little bit more, actually. Call it 520 miles. But no farther."

"You see, when we first noticed this happening, a few days ago--"

"You waited a few DAYS?" I interrupted, a tremor tinging my voice. "And you couldn't send email this whole time?"

"We could send email. Just not more than--"

"--500 miles, yes," I finished for him, "I got that. But why didn't you call earlier?"

"Well, we hadn't collected enough data to be sure of what was going on until just now." Right. This is the chairman of statistics.

"Anyway, I asked one of the geostatisticians to look into it--"

"Geostatisticians..."

"--yes, and she's produced a map showing the radius within which we can send email to be slightly more than 500 miles. There are a number of destinations within that radius that we can't reach, either, or reach sporadically, but we can never email farther than this radius." //

"Well, the consultant came in and patched our server and rebooted it. But I called him, and he said he didn't touch the mail system." //

It so happens that Sendmail 5--at least, the version that Sun shipped, which had some tweaks--could deal with the Sendmail 8 sendmail.cf, as most of the rules had at that point remained unaltered. But the new long configuration options--those it saw as junk, and skipped. And the sendmail binary had no defaults compiled in for most of these, so, finding no suitable settings in the sendmail.cf file, they were set to zero.

One of the settings that was set to zero was the timeout to connect to the remote SMTP server. Some experimentation established that on this particular machine with its typical load, a zero timeout would abort a connect call in slightly over three milliseconds.

$ units
1311 units, 63 prefixes
You have: 3 millilightseconds
You want: miles

• 558.84719
  / 0.0017893979

"500 miles, or a little bit more."