Handling Legacy Outlook Clients with Grommunio Proxy

cigige

Hello

I am testing Grommunio as a drop-in replacement for Exchange in a mixed client environment and encountered strange behavior with older Outlook clients (especially 2013 and some patched 2016 builds). While newer versions using MAPI-over-HTTP connect fine through the Grommunio proxy, legacy clients either hang during autodiscover / fall back to unsupported RPC-over-HTTP modes; leading to inconsistent sync and authentication errors.

I have reviewed the logs and can see partial negotiation; sometimes ending with 401 or redirect loop errors. Disabling proxy or forcing MAPI-over-HTTP sometimes helps, but this breaks usability across the board.

I am wondering if the issue is tied to missing headers, misconfigured fallback endpoints, or Grommunio’s default proxy behavior with legacy protocols. Has anyone found a clean way to bridge compatibility for these clients without fully deprecating support? I checked https://docs.grommunio.com/kb/autodiscover.html with Workday Course documentation guide for reference .

Would appreciate any advice from others supporting hybrid or gradual migration environments. Are there NGINX tweaks / autodiscover tricks that helped in similar setups?

Thank you !!

WalterH

Outlook 2013 reached the end of its life cycle about two years ago. It is best not to use it anymore. Use Outlook 2016 or a more recent version instead. The advantage of this is that Outlook 2016 and later versions use the same code base and therefore the same group policies.