1. Log into WHM.
2. Click on DNS Functions then find the domain you want to edit and click Edit.
3. Where it says Add New Entries, enter the following into the first text box:
_autodiscover._tcp4. You can modify the TTL on the record if you want, or leave it at the default 14400 seconds.
5. Where it says Select choose SRV.
6. Where it says Priority enter:
107. Where it says Weight enter:
108. Where it says Port enter:
4439. Where it says hostname enter the external FQDN of your exchange server:
remote.somedomain.com.10. Click Save button at bottom.
(don't forget the period at the end of the hostname)
11. Use Microsoft's Exchange Autodiscovery tool to check your work:
For more info: https://www.thirdtier.net/2009/02/setting-up-an-external-autodiscover-record-for-sbs-2008/