Exchange 2013 - OutlookAnywhere InternalHostname Change without Disruption

Environment
EXCH01 - All Roles
EXCH02 - All Roles
Three databases setup in DAG.

The problem is when the engineer setup these Exchange servers, he left the FQDN as the Internal Host and OutlookAnywhere address on each server. So if a server goes down, Outlook stops working for many people. I am looking to update all the Virtual Directories and OutlookAnywhere to use mail.domain.com. Normally I would have set this up from the beginning and wouldn't have to worry about it. I don't like making changes without knowing the impact. Right now if you look at the Exchange Proxy Settings in Outlook, everyone is either pointing to exch01.ad.domain.com or exch02.ad.domain.com.

For one, do I need to update the Virtual Directories to use mail.domain.com or can I just update OutlookAnywhere? Once I make these changes on the Exchange server, will it have any impact on the end users, or will Outlook automatically update with mail.domain.com the next time they connect? The SSL certificate already has mail.domain.com listed, but it is currently only being used for OWA via a firewall NAT policy. No External URLs have been setup as I believe they only want people using Outlook internally or through VPN.
Keith PratolaSenior Systems ArchitectAsked:
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Will SzymkowskiSenior Solution ArchitectCommented:
If you update your FQDN virtual directory internally you will also be required to ensure that Split DNS is also setup.

As for the clients there is a possibility that they will be disconnected. If everything is stable if the server do not go down, make this change after hours so you are not disrupting the business.

I have also create a HowTo for configuring the VD's and Split DNS
http://www.wsit.ca/how-tos/exchange-server-2/configure-split-dns-and-exchange-2013-virtual-directories/

Will.

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Keith PratolaSenior Systems ArchitectAuthor Commented:
Thanks. I am aware of the Split DNS. We have been pending approval to make that change for the past month. The client is very slow. OWA doesn't work internally because everyone is trying to use mail.domain.com which isn't available yet inside the network. That is what started me taking a look and noticing that DAG won't even work properly because of the FQDN.
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