Beginning July 22, 2017, secure org connections will be required to use the latest security protocol, TLS 1.1 or higher.
What You Need to Know (Upcoming TLS 1.0 Disablement)
Beginning July 22, 2017, Salesforce will require TLS 1.1 or higher to provide a more secure environment and prepare you for continued PCI compliance. The impact of the TLS 1.0 disablement will vary by org, and depends on the ways in which your users connect to the Salesforce service. Take action now to ensure uninterrupted access to Salesforce. Key areas of impact include:
User browser access – Browser incompatibility will prevent your internal users accessing salesforce.com.
Microsoft email integrations – Integrations such as Salesforce for Outlook, Exchange Sync and Salesforce App for Outlook won’t work if users don’t meet compatibility requirements.
API integrations – These integrations will cease to work if they are not compatible with TLS 1.1 or later. This includes .NET-based integrations that send requests to Salesforce and are not enabled with TLS 1.1 and/or TLS 1.2.