As far as the 500 errors, you might want to check mailbox.log to see why things aren't downloading. Maybe some bad server configuration? Maybe it's just in some loop and continually syncing.
So what I would suggest is to enable ZCO logging (just logging and http logging), and do a run. Your log file will get really huge, so you 'll want to put 0 for the size (in zcologctl.exe), or do the multiple .bak files stuff. In any case, I don't need to see all of the log, but if you could post the last few megs that could be enough for me to see what's going on.
But I think something is not configured correctly somewhere. |