MEG generally only scans traffic on port 25. Google uses other higher ports for their communication, I believe usually 465.
And it can't be added another protocol??
You can add other ports for it to intercept, although if the traffic to Gmail is encrypted, the MEG won't necessarily be able to decrypt it.
Go under Email - Emali Configuration - Protocol Configuration - Connection Settings (SMTP) - Transparent Interception ports
Here you can add additional ports that you want it to intercept.