I was reminded a couple weeks ago about a change that Salesforce had communicated, I want to say maybe a year ago. However in speaking with a customer recently, they had forgot about this API Endpoint change communication so I wanted to share on our communities as well! Great links included from Salesforce as well for more information.
Salesforce has made some changes that went into effect on April 20th, 2018 that may affect some customers if you have an integration with Salesforce.
Customers were able to use www.salesforce.com as an API endpoint that would route them to the correct instance. From April 20, 2018, the internal routing has been retired, and any API endpoints will need to be changed if you are using www.salesforce.com. This only applies to API traffic; logging in from a browser by clicking “login” will still work.
NOTE: This change does not impact API calls to My Domain, Instance, or Login endpoints, such as mydomain.my.salesforce.com, na50.salesforce.com, login.salesforce.com, or test.salesforce.com.