Outbound e-mail hasn't been configured (SharePoint Server)
APPLIES TO: 
2013 2016 2019 Subscription Edition 
SharePoint in Microsoft 365
Rule Name: Outbound email hasn't been configured.
Summary: An outgoing email server hasn't been configured on this SharePoint Server deployment. With no SMPT server configured for outgoing email, SharePoint Server can't send email messages, including alert email, confirmation email, invitation email, and email about exceeding quotas.
Cause: An SMPT email server hasn't yet been configured in the farm.
Resolution: Configure outgoing email settings in Central Administration
Verify that the user account that is performing this procedure is a member of the Farm Administrators group.
On the SharePoint Central Administration website, select System Settings.
On the System Settings page, in the E-Mail and Text Messages (SMS) section, select Configure outgoing e-mail settings.
On the Outgoing E-Mail Settings page, type the SMTP server information in the Outbound SMTP server box, and then specify the addresses and the character set that you want to use.
Select OK.