Mail protection and Transparent Proxy (not MTA)

Question

How can I set the Sophos XG mail protection, acting as a Transparent Proxy?

I prefer receive mail from internet to my mail provider server, and so downloading them using POP3.
I'm a bit worried to set the XG as MTA, in case of XG failure all the received mail should be lost.

Is there any official guide?
I've just found a lot of "how to" or threads for the MTA mode.

Thanks

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lferrara · Answer

Simone, 
 from Email Menu > General Settings > SMTP Deployed Mode > Make sure XG is acting as Transparent 
 Create a Pop3 policy under Email >Policies TAB 
 and make sure to create a Firewall Rule that filters Email using a New Business Application rule > Email Client Template where the source zone is LAN and Remote is WAN. 
 Take note that XG is not able to block SPAM when it acts as transparent proxy, but it can only change the prefix subject (you will find it under Action inside the POP-IMAP email policy). 
 Vote the feature request: 
 https://ideas.sophos.com/forums/330219-xg-firewall/suggestions/10614834-pop3-imap-more-scanning-option 
 Regards