IMAP is a protocol that is used with natively installed mail clients such as Thunderbird, Apple Mail and Outlook to connect with Google's mail servers. To see a complete list of supported clients please see this resource for more information.
The key difference between using IMAP and the Gmail web interface is that with IMAP you are actually dealing with files that have a bit of size as oppose to links inside of a browser with the Gmail client. Oftentimes, you'll want to reduce those file sizes to something that is a bit more manageable when you start dealing with a lot of mail messages. Because it's probably never a good idea to have mail stored on your machine in the multiple gigabyte range.
Here's what you need to do in order to reduce this down.
In your inbox, head over to your Mail settings on the upper right hand side of your screen.
In settings, head over to the Labels tab. At the top of that tab, you will see settings for your labels, on the right hand side you can see that these labels will also be shown in your IMAP client as well.
You can uncheck any of these to reduce the size, but your best bet is simply to uncheck the "All Mail" label.
The file size for you main inbox should go down significantly - and this is certainly an easy fix to implement across many computers. Have you ever experienced this particular problem, and did not know how to change the file size until now? Labels: changing IMAP options Google Apps, IMAP Google Apps, IMAP mail clients
