You may experience this message when setting up an email client to use with your company email address.
The symptoms at this stage are typically that you can receive mail, but not send. The solution to issue is almost always that you haven’t given the email client (e.g. Microsoft Outlook) the instruction to authenticate the outgoing server. This is very easy to do in most email clients and once the correct details are added to the configuration settings the issue is usually resolved. In most cases, the details are simply your email address and password as you’ve already input for the incoming server.
Step 9 on the How to configure Microsoft Outlook to use your company email tutorial gives an example of this setting for Microsoft Outlook.