IMAP mail transfer to new host

[Timothy Murphy]

I want to use imapsync to transfer my email
from ~tim/Maildir/ on alfred to ~tim/Maildir/ on helen ,
all internal to my system.
Can some kind soul tell me the command to give on helen .

I've tried different variants, and get various errors.
I should say that helen is running Centos 5.2
while alfred is running Fedora-8.
I'm changing servers from alfred (an ancient machine) to helen.

All advice or suggestions gratefully received.