Classilla Mail Speed Issues

[Milko]

I've just finished setting up Gmail on the built-in mail client on Classilla, after a pretty painful process downloading all the messages (took about 2 hours and the system locked up a few times) it seems to be working well now. The only problem is that every 30-40 seconds, the mouse cursor turns to the little stopwatch and it sits there loading something for about 20-30 seconds, during this time Classilla stops responding. This begins happening as soon as I open the mail client and won't stop unless I quit Classilla and restart.

Could this be caused by a large mail inbox? I have about 9,500 emails in it. If so, is there a utility in Classilla that can be used to archive the old messages?

[ovalking]

Just opening the mail client doesn't cause any problems for me, but I only have the odd message.
There's a Compact Folder item in the File menu, but that may be more of a 'defragment' rather 'compress' type function.
I prefer Netscape for mail, much less demanding for the Mac.