Which of the following methods is not a secure way to connect clients to Exchange?

Which of the following methods is not a secure way to connect clients to Exchange?

• Outlook using MAPI/RPC
• Outlook Web Access over HTTPS
• Outlook using RPC over HTTPS
• Outlook using IMAP4 with SSL 

EXPLANATION

The point they're making is that "traditional RPC" sometimes uses unusual low-level network protocols that often get blocked by corporate firewalls. Because SOAP uses HTTP, it's traffic is "indistinguishable" from normal web page views, and so is not caught out by these firewalls. Not too sure about the security point, I think they're probably implying that HTTP can easily be secured over HTTPS and that proprietary RPC protocols often don't. Of course, this is protocol dependant, not all RPC protocols will be insecure, and many of them can be tunnelled over HTTPS.

RPC over HTTP, also known as Outlook Anywhere, is a legacy method of connectivity and transport between Outlook for Windows and Exchange. In May 2014, Microsoft introduced MAPI over HTTP as a replacement for RPC over HTTP.
Starting on October 31, 2017, RPC over HTTP will no longer be a supported protocol for accessing mail data from Exchange Online. Starting on this date, the following conditions will apply:

1. Microsoft will not provide support for RPC over HTTP issues (regular or custom).
2. No code fixes or updates to resolve problems that are unrelated to security will be released.

Additionally, for Office versions that support MAPI over HTTP, Microsoft may elect to ignore existing registry keys that customer are using in order to force RPC over HTTP use.