[RKDinOKC]

Make sure autodiscover is configured correctly both internally and externally.

in 2010 MS used web access for PC/Mac Outlook and OWA so dns server name is mucho importanté.
Phones use ActiveSync besides different ports active sync can be handled by different servers/IPs.

With more modern Outlook it now uses autodiscover to find where the server is located. That way it can be moved around for availability and server maintenance. So your DNS/IP address might be finding a server, but not one that is currently hosting your domain.

It looks like they are moving toward everything using active sync.

Until about 6 months ago my desktop would chime letting me know Outlook had received a new email. The in about 3-5 seconds my phone would ding letting me know the new message had arrived. Now it is much different. My phone dings, and then the message arrives 20 to 50 seconds later to my desktop Outlook.