the "Account exceeded bandwidth limits." is a message which comes from Hotmail or Gmail IMAP server. Probably (but I'm only guessing) your application is download so much content that it triggered this error.
Following post at Google support forum is discussing this exact topic: http://www.google.com/support/forum/p/Google%20Apps/thread?tid=0ece6b37ff80c552&hl=en
I would recommend modifying your application so it downloads the message more slowly. For example pause your application after each message download for some time.
Alternatively you can try to ask Google/Yahoo if bandwidth limit for your account can be increased.