The Preferred Connectivity Protocol for Exchange Online

In November 2016, Microsoft told Office 365 customers that they would no longer support RPC over HTTP (aka “Outlook Anywhere”) connections to Exchange Online. The idea was that if customers had almost a year to upgrade clients, Microsoft could hit the switch on October 31, 2017 (today) and everyone would move forward into a new world of MAPI over HTTP connectivity.

Customers Said No

As it turns out, life is sometimes difficult, and customers do not cooperate. Pushback from customers has forced Microsoft to soften its stance. Instead of a total ban on RPC over HTTP connections, Microsoft will cease supporting the protocol in a gentler attempt to convince customers to move their Outlook connectivity to MAPI over HTTP.

Although RPC over HTTP connectivity will continue after today, it will no longer be a supported protocol. This means that Microsoft will no longer offer support for any issue connected with RPC over HTTP and will not release any code fix or update to resolve problems, except when those problems compromise security. Nothing dramatic will happen when Microsoft ceases support. RPC over HTTP connections will continue to work, and Outlook will be able to send and receive email.

The Problem of Old Outlook

The problem facing customers is quite simple. Large populations of older versions of Outlook are in daily use and customers have no appetite to refresh those clients. Desktop refreshes are always (un)popular with I.T. departments. They are complex, costly, and usually involve some user retraining to master the details of the new version of Office. In turn, the help desk gets more calls, which drives more cost.

Despite Microsoft’s best efforts to convince Office 365 tenants that Office 365 ProPlus, the click-to-run version of Office, is the best choice, customers often take the sensible approach of “if it’s not broken, don’t fix it” and persist with Outlook 2013, Outlook 2010, and even earlier clients.

Proving the longevity of the protocol, all Outlook clients can connect using RPC over HTTP, but not all clients can connect using MAPI over HTTP. For instance, Microsoft never backported the new protocol to Outlook 2007, so Outlook 2007 and earlier clients instantly become unsupported when Microsoft stops support for RPC over HTTP.

Check Your Clients

If you are unsure about the supportability of the clients you use, check the system requirements for Office 365 for more information and this page for the latest updates for Outlook. Essentially, the best idea is to run the latest version of Outlook you can, complete with all available updates.

Microsoft recommends that tenants only run clients that support MAPI over HTTP. This makes sense given that no future development will happen for RPC over HTTP, its unsupported state, and that Microsoft has no interest in the protocol.

Cloud Plumbing

As I noted last year, the transition to MAPI over HTTP is an example of Microsoft upgrading its internal plumbing to make the cloud function better. Old email protocols sometimes die hard (IMAP4 and POP3 are great examples), but the writing is on the wall for RPC over HTTP.

Follow Tony on Twitter @12Knocksinna.

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