Unjustified "Mailbox is at XX% of quota" messages in Thunderbird

[Kővári János]

Hello all,

I have a problem again.
Just today, all my users, who are using the same shared folder, are 
getting "Mailbox is at 93% of quota" (and increasing as they put mail 
into the shared folder) messages in Thunderbird (v.2.0.0.24 on Vista X64).
This has started when one user was putting several dozen bigger emails 
into the shared folder, which then reached a "mysterious" level, where 
warnings are sent out.
The problem is: this shared folder has a 5GB quota limit and it contains 
~930MB of mail only. The quota file says 5GB, Thunderbird says 5GB, 
Cyrus module in Webmin also says the Quota is 5GB, and the usage is at 
19%...  Everything says the Quota is 5GB and it is 19% used. But the 
messages still pop up.
It seems, the server somehow thinks the quota is 1GB, of which indeed 
93% is in use, but I have no clue where this comes from. It can't be 
confused with user mailbox quotas, because those are at 200MB.
The shared folder is stored on a separate partition with hundreds of 
gigabytes of free space.
I have reconstructed the mailboxes and folder, and re-checked the quotas 
etc.

If anyone has any ideas, I'd be glad to read them! Thanks in advance!

Regards,
Janos