Exclusive Ever become stuck in a seemingly infinite loop of emails from colleagues hitting the "reply-all" option and asking to be removed from a mailing list containing the addresses of thousands of employees?

If the answer to that question is a resounding yes followed by a massive sigh, then you ought to have some sympathy for Cisco, whose staff - The Register understands – wasted an estimated $600,000 at the networking giant after unwanted messages began to stack up in their inboxes.

The "reply-all" email storm ended only after Cisco's IT bods pulled the plug on the list, we've been told by an anonymous source.

At that point four million emails had been sent, generating over 375GB of network traffic, our insider claimed. The deluge of messages apparently peaked at five emails per second.

The time-wasting among the 23,565 Cisco peeps was calculated by our mole as costing the company more than half a million dollars in precious productivity.

What went wrong?

On Wednesday, an employee at the San Jose, California-headquartered company, sent an email intended only for a small set of managers that nagged them to nag staff about completing an online training module by the end of the month.

But, in a move reminiscent of other email storms*, the unnamed sender mistakenly included a "sep_training1" mailing list that contained the addresses of thousands of Cisco employees – presumably without a restricted senders' list.

We were told:

While the managers were discussing if the training was relevant to their staff (keeping the mailing list in the 'To:' line), someone triggered the storm by asking to be removed from the mailing list. It gathered momentum, mainly from the Indian offices, with lots of 'unsubscribe' and 'me-too' requests, followed by irritated people asking everyone not to reply-all (while doing so themselves). In among this, there were various sarcastic facepalm images and silly suggestions such as people needing to respond with an unsubscribe haiku to be removed from the list. Just when it looked like the storm had ended, it quickly picked up pace again as employees in the US opened their mails in the morning.

Cisco isn't having a good month: It is set to axe up to 4,000 staff (about 5 per cent of its headcount) at the tech giant, its chief John Chambers confirmed last week.

El Reg asked Cisco to comment on this story. A spokeswoman at the firm told us: "I personally didn't see the email so can't comment." ®

* Who remembers Bedlam DL3 at Microsoft? Oh, and Cisco is, it would seem, something of a pioneer in the email storm phenomenon.