The differences between SNAT and DNAT

Question

Dear Wizards, I'm a newbie to Sophos XG Firewall, can I ask the differences between SNAT and DNAT? In which case which method should we use? 
 For example: we have some Exchange mail servers, Web servers, ERP servers, SharedFile servers then we should use DNAT, am I right? 
 Many thanks in advance!

Charmacas · Answer

DNAT: Traffic from various IPs is being forwarded to a specific internal IP. Example: You want your internal Webserver to be available through the internet. 
 SNAT: Traffic from various IPs in a certain direction should only show a specific IP. Example: You want to reach a network over VPN but the remote network should only see a specific IP so you're hiding the internal IPs behind the IP configured in SNAT. 
 I hope that makes sense for you.