Sophos XG, SPX & Mimecast Cloud Mail filter & Archive

Hi,

Has anyone had any experience in setting up Sophos XG firewall to use SPX email encryption where an existing mail flow is from an internal exchange server to Mimecast who then deliver the email to the intended recipient?

Our exchange server is configured currently to only send and receive email traffic from Mimecast's servers and it works fine. After setting the XG into legacy mode I have been able to test a Business Application Rule to scan incoming SMTP traffic, but as Mimecast have already scanned it I'm not to worried about that side.

What I'm more interested in finding out is how the outgoing, with encryption could work. Ideally something like the XG intercepting outgoing emails heading to Mimecast from our server. The XG doing it's encryption thing and sending the new message on it's way to the recipient. I then expect the recipient will be able to navigate directly back to the portal to configure a password etc.

Does this sound possible?

Any ideas?

Thanks.