EAS proxy in powershell mode for onpremise exchange server secure enough?

Question

Hi Community, 
 we are evaluating sophos mobile central for securing exchange active sync access to onpremise exchange server. 
 
 Question 1: Is EAS proxy in powershell mode for onpremise exchange server secure enough? 
 As noted in documentation in powershell mode there is direct connection to exchange server. So only authentication is controlled by EAS proxy and there is no additional security wall/shield between internet and exchange server. I think about vulnerabilities can exploited without authentication. 
 I think this powershell mode is secure enough with exchange 365 in microsoft cloud, but is it secure enough in connection with onpremise exchange server. 
 Are there some opinions? Is real proxy mode more secure at all? 
 
 Question 2: Is it possible for internal unmanaged devices to connect directly to exchange server by exchange active sync when using EAS proxy in powershell mode? 
 
 Thank you. 
 Kind regards, 
 Chris

Qoosh · Answer

Sophos22 said: there is no additional security wall/shield between internet and exchange server. 
 Could you elaborate on this a bit further? 
 The EAS Proxy will ensure the connections established with the Exchange Server are secure in terms of the mobile devices or workstations that connect to it to retrieve mail. If you wish to have additional protection on the server locally, you will need to have Sophos' Server Protection deployed on the system as well. 
 If you wish to prevent any unmanaged devices from connecting to the exchange server, you can also use the steps mentioned in the following article. - Block email access for unmanaged devices 
 If you are in the early stages of trying out Sophos Mobile, I'd also suggest trying to connect with your regional Sophos Sales Engineer to see if they can work with you to demo out the features you're interested in. You can engage with your Sales Engineer by first reaching out to your Account Manager. If you'd like assistance in finding out who that may be, please send me a private message and I'd be happy to help.