Lync Mobility: E_ConnectionError E2-2-1


Lync Mobile Client won’t sign in.
Mobile client logs contain the error E_ConnectionError E2-2-1
Tests from are failing.

Lync Mobile Error E2-2-1

 What we do know from

  • the DNS record is resolving correctly
  • the TCP port 443 is allowing the connection
  • the SSL certificate seems to be OK

This means that we have made it onto the Reverse Proxy.

What appears to be failing is the jump from the Reverse Proxy to the Front End.

Following the Tell me more about this issue and how to resolve it link lands you on the following page

Mobitliy Issue E_ConnectionError (E2-2-1)

To be honest , that’s actually rather solid information from Microsoft..let us take a deeper look at this info

A Network Error Occurred while Communicating with Remote Host (Front End)

  • The server is down.
  • The specified port is not listening for TCP connections.
  • A firewall, proxy server, or hardware device is blocking the connection to your server.
  • The network is congested.


So what the underlying issue here boils down to is that for some reason the traffic is not reaching the Front End Server from the Reverse Proxy.

Of course this could be that the Reverse Proxy is incorrectly configured.

From my experience, the most common causes in a new deployment are:-

  • Reverse Proxy cant resolve the host name for the Front End
  • Ports are blocked (from Reverse Proxy to Front End port 4443)
  • Forgot to port forward 443 to 4443 (or 80 to 8080) on the Reverse Proxy


The E2-2 errors usually refer to a connectivity issue. E2-2-1 generally means that the client couldn’t reach the destination.


When you get redirected to a hyperlink do take the time to consider the common causes. Who knows, you might even find the answer..


About Paul B

My name is Paul Bloem and I am employed at Lexel Systems in New Zealand as a Principal Consultant for Unified Communications. I have been working on enterprise voice solutions for over 20 years. My first 10 years were spent working for a Telco in South Africa (Telcom SA). This is where all the groundwork happened as I was exposed to just about every aspect of telecommunication you could imagine. I develop an interest in PBX technologies and eventually became the go-to guy. Next, I had a 10 year run at Siemens South Africa, most of my time there was as a Technical Trainer. During this time VoIP hit the world stage, I had the privilege of introducing VoIP both as H.323 and later SIP across the Siemens HiPath 4000 solution stack. In 2008 I immigrated to New Zealand with my newly attained MCSE, I was ready to go where no PBX Techie had gone before. I was employed to explore OCS 2007 and that was pretty much the beginning of the end for me. I have been working on OCS and Lync ever since. My current role focuses exclusively on Lync and associated technologies.. That includes pre-sales, consulting, architecture and design, training and support. I even get to play in the development space from time to time - focus on play ;-) I was nominated as a Microsoft VTSP for Lync early in 2013 and also awarded Microsoft's MVP award for Lync in 2014.
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