We have iPhones that synchronize theirs mail and calenders against our Exchange 2007(owa).
The users complain sometimes that the sync doesn't work between the iPhone and the Exchange server(owa).
I got a lot of this in the access_log
webmail.xxx.yy 184.108.40.206 - -
And these in the error_log
Wed May 30 12:54:25 2012 error http://client 220.127.116.11 proxy: error reading status line from remote server owa.xxx.yyy.zz
Wed May 30 12:54:25 2012 error http://client 18.104.22.168 proxy: Error reading from remote server returned by /Microsoft-Server-ActiveSync
Can it be that we have an old version of HTTP Server? It's only the owa that having the problems, other addresses works fine.