Slow local network performance for image attachments

[Jeff Larsen]

I run cyrus imap in a virtual machine at home using fetchmail to pull
my ISP mail into a local imap store. For the most part it works great.
But with messages that have digital photo attachments it takes a
seemingly inappropriate long time for Thunderbird to download the
message (over local wired 100Mb network) and display the pictures.

I've got plenty of memory overhead on both the virtual machine and the
VMware Server host. While in the process of downloading an image
email, the CPU usage goes higher than I would expect (20%) for a
simple file transfer. It takes 10-15 seconds to load a message with 3
images totaling  5MB over non-encrypted port 143. It's 2 or 3 times
that long if I use imaps on 993.

The VMware host is a 2GHz Pentium, with very little load from other processes.

What's gong on here and can I do anything to fix it? Why so much CPU
to transfer a 5MB message?. Doesn't Thunderbird handle the mime
decoding?

We use a similar setup at work (cyrus on virtual machine) for 50 users
and I don't have the same problem there. Granted, the hardware is
faster, but it's also carrying a much heavier load for other services.

-- 
Jeff