./imapsync --buffersize 8192000 --nosyncacls --subscribe --host1 10.10.100.15 --user1
user@domain.com --password1 userpassword --host2 zimbra1.zimbraserver.com --user2
user@domain.com/tb --password2 userpassword --authmech2 LOGIN --sep1 . --prefix1 INBOX.
| tee user@domain.com.log
i use above command to migrate from Imail to Zimbra.. you can see in the end it will send all output to log.
if you have lots of emails..log is big.
for me its shows all communication which happens when imapsync is running
Raj