Need help configuring gmail

There is not.

The reason is explained here: 

https://community.sophos.com/kb/en-us/132997

(The KBA is for HTTPs but Email performs the same kind of TLS Inspection). 

I thought that transparent mode did not decrypt/encrypt the mail packets?

If you do not tick any of the boxes in transparent mode nothing goes through the rule. You can tick smtp, but you will need a seperate firewall rule for smtps.

Ian

In SMTP Transmission, StartTLS is nearly the first command. So after this, a Transparent proxy needs to break the TLS to take a look into the stream. 

https://en.wikipedia.org/wiki/Simple_Mail_Transfer_Protocol

Perhaps I should re-phrase my question. Is there any way to configure XG firewall to scan incoming (and if possible outgoing) e-mail with out having to install custom certs on all of my machines?

Hi Donald,

you will need to install at the very least the XG certificate if you want to use smtps and HTTPS scanning on the XG. Without the certificate your users will get failure to connect issues.

Ian