Thunderbird barfs at about 4 gigs. As in it won’t let you receive any new email and you have to dump your folders and start over.
I keep my “community” email separate from my business one and just take it for granted now that when I get to that magical 4 gig mark, it’s time to start a new folder structure.
Actually its an OS limitation.
Limits – Thunderbird – MozillaZine Knowledge Base:
http://kb.mozillazine.org/Limits_-_Thunderbird
Limitation of the product.
Actually if you read the KB article referenced by “bradley”, you’ll see that the T-Bird 4GB limit is a limit on the size of a FOLDER. The mailbox has unlimited (well, up to the available disk space) size.
And I think people’s main concern was *Exchange* mailbox size. In exchange if you put a few thousand messages in a folder performance degrades badly.
I once saw an Outlook PST that was 20GB…very long story
I know it’s not quite the same as having all that data in an Exchange mailbox, but it was painful anyway