There are a number of ways you can achieve this:
Outlook Xplan Plugin
Refer to Article How do I install the Outlook Plugin V2/V3? | Centrepoint Alliance Technology Solutions (cpal.com.au)
Email forwarding
'Remote filing' is simply the act of pushing content into XPLAN when your not using XPLAN.
Via Group Id forwarding
Direct Client Forwarding
The client's unique XPLAN email address will be their entity id @ your XPLAN site name.
You can find the Entity I.D
*Your Site Administrator will need to enable this functionality on your site and you will need to have email address white listed.