We have an Apache 2.4 (SLES 12) sitting in front of our GroupWise WebAccess
(2014 R2 SP2). All in all that works, but we have a lot of error messages
like this in the log of the reverse proxy:

[Fri Jul 21 15:03:46.736290 2017] [proxy:error] [pid 1133] [client
xxx.xxx.xxx.xxx:46888] AH00898: Error reading from remote server returned by
/gw/webacc/poll, referer: https://webmail.hs-offenburg.de/gw/webacc

[Fri Jul 21 15:04:46.928301 2017] [proxy_http:error] [pid 1133] (70007)The
timeout specified has expired: [client xxx.xxx.xxx.xxx:46888] AH01102: error
reading status line from remote server webmail_int.hs-offenburg.de:443,
referer: https://webmail.hs-offenburg.de/gw/webacc

I am trying to understand what this access to "/gw/webacc/poll" does or
should do. "Polling" as far as I understand is done from WA server to POA,
not from Client to WA? Autorefresh works fine. So "poll" here refers to
another kind of operation?

I see these messages every 60s (for every client connection), but I have
also seen them every 1s. I don't see any corresponding error on the WA
server, I only see it in the access log.

Any idea what /gw/webacc/poll does and what might go wrong with proxying
especially for this part?