An interesting little issue with a client's configuration caused a problem recently.
The problem only affected users off site using Outlook Anywhere. While they could get their email correctly, the availability service didn't. This stopped Out of the Office from working correctly unless OWA was used, or the end user was in the office.
This particularly configuration uses a Client Access Server in a data centre, which proxies over a site to site VPN in to the main office where another CAS, plus the mailboxes are actually located. Therefore the issue had to be around a configuration difference between the two servers.
get-clientaccesserver servername |fl
on the server in the data centre and comparing it to the server in the main office, showed that the value for AutodiscoverSiteScope was populated with the AD site for the main office. This was because the server in the data centre had been built in that location initially and then moved.
Removing that entry so it was blank resolved the issue:
Set-clientaccessserver servername -AutodiscoverSiteScope $null
A five minute fix resolved an annoying problem for the end users.