When you attempt to do the EMAIL instruction (or whenever a PC (or phone for that matter) attempts to send/receive email, the first thing it does is establish a TCP connection. This is nothing that you do manually; it is something that is done automatically. But it is fundamentally the FIRST thing that needs to happen. If a TCP connection cannot be established, then the process does not even get to the email part. Thus, when I mentioned that a TCP connection is not being established, this is very fundamental and is merely indicative that the very basic connection is not happening. Bottom line is that it simply means, for whatever reason, your PLC cannot "see" the email server to even establish the fundamental connection. All this is basic TCP stuff and not unique to BRX or Do-more.
So, basically what this means for your particular scenario is your PLC cannot contact 173.194.198.27 (aspmx.l.google.com). What are the IP settings (IP address, subnet mask, gateway address) of your BRX? You can see these by going to the Dashboard and moving your mouse over the Ethernet port. You'll see something like the pic I have attached. Or you can use the menu and select PLC --> System Information, and click on the <Set Node and IP Configuration> button.