I've changed the limits on zimbraFileUploadMaxSize and zimbraMtaMaxMessageSize to allow files up to 500MB. When on the local network with our Zimbra box, I can easily upload files with no problems. 400MB ISOs are stored just fine. However, when trying to upload a larger file from an offsite location, odd errors occur. The upload speed at the remote site is roughly 512k. When trying to upload a 200MB file, Zimbra churns and churns during the upload process. When complete, there is no notification and the file never shows up in the briefcase. Smaller ~10-50MB files have no problems.

I can verify that the entire file transfer completed successfully by checking the traffic usage on our edge firewall/router. I've even tried logging in and out, clearing the local browser cache, etc with no avail.

Is there some sort of timeout mechanism for the transfer? When transferring a 200MB file over 512k DSL, it can take a bit of time for the transfer to complete. Maybe a socket is closing prematurely within Zimbra?

We're running Zimbra OpenSource 5.0.4_GA_2101.RHEL5 on 32bit x86 CentOS5.

Where would you start to troubleshoot such a problem?

All ideas welcome. Thank you!