What you are speaking about is an airgap, a device or network with no network connections outside of its own loop.
If you had an email client within the airgap then you could view emails that have been transferred over to the airgapped system on removable media, but you could still be infected by any malware that is contained within them.
A well known example of this is the famous 'stuxnet' malware. Although the exact delivery mechanism was not email, it was targeted malware that was suspected to have breached the airgap via removable media.
The airgap itself will mitigate against many types of malware, even if it is successfully delivered. For example, droppers, c2 bots and other malware that requires an Internet connection to function and/or spread will not be able to function correctly.