Claranet: big
I am a Claranet customer, have been for eleven years, and the only other interruption to service I have suffered on this scale in that time was when BT-operated facility in Ilford caught fire, and broke an awful lot of wholesale ADSL, not just Claranet's.
This is/was not rebuild a POP server. The error message displayed on the webmail login page for a time was: "We are currently experiencing service problems on the Claranet E-mail platform. Claranet Engineers are currently working with our Storage Vendor to rectify the situation.We regret any inconvenience this may causing you."
Claranet, between the business services and the retail services and the services shared with other ISPs they have bought or with which they have partnered, is pretty big. A lot of their stuff used to run on FreeBSD on SPARC hardware; I don't know how much of what still does. It always appeared to me, based on there being multiple public server names that one could use to configure sending or retrieving mail, that there were actual different internal servers providing redundancy and they were all capable of reading to or writing from the same disk files for serverside mail filters, mail filter logs, POP3 mailboxes, and so on -- presumably these files were in some way on a network share, which is not a configuration I'd have chosen, but then what do I know, never having had to spec up a mail handling system even a thousandth the size of this one.
"currently working with our Storage Vendor" I'm going to take a punt: that is to say, the controller card for the RAID went bang, the guy from Sun turned up within x hours as per the Gold/Enterprise/WeLikeJonathansPonytail -level support contract, and yet somehow, despite the customer having the biggest best support contract available, despite knowing what hardware the customer had, despite being told by the customer what component on what system had failed, the guy from Sun did not have the required part on the van.
The interruption to service was a nuisance. As best I can tell no incoming email was lost, and I (and every Claranet customer I know personally) had workable alternative provision for sending and receiving email. The biggest bitch I have right now is that the serverside mail filters aren't available and so 90% of the spam I get sent ought to be deleted before it hits my POP3 mailbox, but currently it's being delivered instead. Anybody want a stack of pointless emails from the likes of sue@casimme.co.uk punting ' ...Business seminar informmation'?