Untangle 6.0 causes Yum updates to fail

As part of our normal on site routine, I ran yum check-updates on a client's CentOS5.1 server today and got back a slew of updates that were needed. When I ran

[root@tux ~]# yum update

I got a pile of errors about incomplete headers.

After a bit of Googling, we found this link: http://forums.untangle.com/showthread.php?t=468 which described our issue to a "T"...

The short lesson is: if you're using Untangle 6.0 in front of a Linux box with Yum, you need to uncheck the "Disable FTP download resume" and "Disable HTTP Download resume" boxes in the Untangle config:

Virus Blocker -> Settings -> Web tab -> Advanced Settings -> Disable HTTP Resume

Virus Blocker -> Settings -> FTP tab -> Advanced Settings -> Disable FTP Resume

The issue is that Yum only wants to download the first 'nn' bytes of the RPM (the header portion) and not the whole file. The proxy server in Untangle overrides this and downloads the entire file (how else to scan the file for viral content, right?). But by downloading and transferring the entire file, it sends too many bytes of data to Yum which is only expecting header data, causing Yum to complain about invalid headers. Apparently this can also cause issues with Mozilla Thunderbirdand and other IMAP clients when they try to download the message headers only (i.e. not the entire message).