Has anyone else experienced this?

From today the Mail app started requesting my password for account "abc" on every attempt to check for new mail on the account server - not too unusual as it will do this from time to time.

The problem started when I suddenly got 180 'new' emails in my inbox. On checking these, they were all old emails that Mail had previously downloaded from the server (they were not deleted, as i had deactivated this because i was away from my mac for a month and wanted to be able to access them via web mail). Each of these 'new' emails were duplicated twice (3 times including the original copy).

I deleted all of the duplicate copies, and put it down to binary weirdness (computer clock time should be ok, as there have been no recent kernal crashes or unplanned shutdowns, or anything else i can think of).

Then, five minutes later (new Mail check interval) i received two copies of the same emails again (180 in total) all of the original dates of these emails were the same as the dates i originally received the emails, some dating back four weeks.

I deleted these again, and then told Mail to delete immediately all server copies of downloaded emails. Problem solved...for now.

The reason i am posting here is that this evening a mate of mine also with a mac emailed to ask what to do as his Mail app was going bonkers with the same problem, only he was getting 700 in his inbox.

What would cause this? Why would it effect both of us at the same time? has anyone else experienced this?

I did just think that it was that neither of us had deleted server copies of emails recently, but i dont know why this would matter, i was no way near the server capacity, i doubt my mate was either. Another panic thought was that it was some malicious action, but i dont know.

Any feedback or thoughts on this would be appreciated.