Yay, a question on this list I can answer. That happens so rarely. Of course, this is completely OT for this list, so maybe that's why... :-)
RFC 2087 defines the quota extension for IMAP:
The Net::IMAP module appears to support this extension.
But, I haven't used that module. It's at version 0.02, and it didn't build and test cleanly for me using 5.6.0. Even so, it may be worth a look.
sherm--
C programmers never die - they're just cast into void.
