More new kit causing havoc
In the days of Windows 3.1 and Netware servers, I was providing support to a large organisation which used Ye Olde Microsoft Mail. Normally it worked fine, with most problems involving failure of comms between two "postoffices".
On the run up to Christmas one year, the whole system died. No emails going in any direction. Mail clients hung on startup.
It turned out that someone had got hold of WIndows 95 and stuck it on the network, without permission. They had also started to use its supplied email client, which talked to the Microsoft Mail Postoffice.
However it lacked some of the restrictions of the earlier software.
The user had sent a 5 line email, warning people to book taxis early in the run up to Christmas. To everyone.
The list of recipients went over the 64K limit enforced in all earlier versions. Clients would overflow their buffers and start again.
The only way out was to physically visit each of the 40 or so Postoffice machines (no remote control software in those days) and delete the offending message file from its drive. Luckily you could work out which one it was from the size.
The fix was of course not covered under our contract, being obviously "User Error".