imapsync very poor performance

[Christian Hügel]

i,

I´m running imapsync-1.569-1.el6.noarch on a Centos 6.5 x64 system with 
8GB RAM and a dual 3Ghz AMD cpu. The sync runs on the "target server and 
the source server is a dovecot 1.2.1
Here are some stats:

0.01 msgs/s 63.780 KiB/s ETA: Mon Dec 2 22:31:21 2013 28528 s 328 msgs 
left
0.01 msgs/s 65.135 KiB/s ETA: Tue Dec 3 01:17:36 2013 38356 s 327 msgs 
left
0.01 msgs/s 65.076 KiB/s ETA: Mon Dec 2 21:44:20 2013 25560 s 326 msgs 
left
0.01 msgs/s 65.238 KiB/s ETA: Mon Dec 2 23:08:44 2013 30484 s 325 msgs 
left
0.01 msgs/s 65.181 KiB/s ETA: Mon Dec 2 21:26:25 2013 24344 s 324 msgs 
left
0.02 msgs/s 65.122 KiB/s ETA: Mon Dec 2 20:18:12 2013 20251 s 323 msgs 
left
0.02 msgs/s 65.235 KiB/s ETA: Mon Dec 2 19:46:36 2013 18332 s 322 msgs 
left

and the cpu is during the sync at 100% The size of the mails are normal 
no attachments so I realy don´t know where´s the issue here.
The size of the mailbox is only 300MB but I have a couple of huge 
mailboxes (>17GB). With this speed it´s quite impossible to migrate my 
mailboxes to the new kolab 3.1 server

Can you please help me out with this issue? Thank you

Christian