Office 365 - loads of attempted logins to non-existent user?

[Sheepshanks]

I can understand people picking up known user names and trying to get in, but I noticed that there are a large number of attempts against urh@.... which is a sequence we've never used (or anything even in the same format).

Every one is from a different IP address, and they're generally at 9 minute intervals.

I asked our IT provider and they seem completely unconcerned, but it's bugging me wondering what someone is trying at achieve - anyone any idea?

[mattley]

Probably from a bot net that's lost is C&C or has just broken.

[Sheepshanks]

C&C - Command and Control - ie it's not working as it's supposed to?

What should it be doing?