Outlook 2016 slow when connecting to Nexus Exchange

We’ve had reports from some Nexus users that Outlook 2016 can appear to hang while trying to make a connection to our Exchange servers. The reported delay is between thirty and forty seconds, after which the connection is established and normal service resumes.

People who have stayed on Outlook 2013 don’t generally encounter this issue, but if they do they can easily resolve it by tweaking settings.

Here is what’s going on: the Exchange 2010 Autodiscover service tells the client to try a regular RPC/TCP connection before resorting to a RPC/HTTP connection. 

In Outlook 2013 there is an option in the program’s settings: ‘On fast networks, connect using HTTP first, then connect using TCP/IP’. This setting resolves the issue (and these days ‘fast network’ means any connection that’s faster than dial-up).

But if you’ve updated to Outlook 2016 that option has disappeared. Essentially you’re looking at a mismatch of versions – Microsoft are assuming that Outlook 2016 will be connecting to Exchange 2016. Once we’ve migrated to Nexus365 we will be but, currently, we’re still on Exchange 2010 on-premises. In other words, even with our best-practice server configuration, newer versions of client software are creating ‘gotchas’ for us…

What can the Nexus Team do about this?

There is an option of mandating all Nexus client connections to use HTTP first. This is a server-side setting we can apply. However this has an adverse effect for everyone who doesn’t use Outlook. For us, that’s a lot of people. We have had to rule out that solution.

The longer-term solution is to migrate our users to Nexus365, since that will effectively bring the servers you are connecting to bang up to date. Pilot migrations begin next month.

What can I do about this?

The recommendation for University IT Support Staff is to use Group Policy to resolve this wherever possible – the policy settings that are equivalent to Outlook 2013’s tickboxes still exist. Microsoft may have removed the interface to see them in Outlook 2016 but the configuration can still be made, albeit via a circuitous route.

The setting you want to change is:

User Configuration\Administrative Templates\Microsoft Outlook 2016\Account Settings\Exchange

Enabling ‘flag 4’ is equivalent to ticking the checkbox in Outlook 2013 for using HTTP first.

Self-managing Outlook 2016 users can edit their registry to achieve the same effect. You need to create (or modify) this key:


Add a DWORD value of ‘ProxyServerFlags’ with a decimal value of 47.

Note that because this is a current-user setting you will also need to apply it for other users of the same PC.

If the problems persist, for multiple users, please verify that your DNS settings are correct for autodiscover to successfully resolve your unit’s subdomain. Even after all these years since Nexus went into service we still find occasional pockets of users putting up with slower-than-needed lookups and configuration challenges which are avoidable with autodiscover set correctly.

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