Alert email notifications are not send to email addresses of an employee and manager

Summary:

Alert email notifications are not send to email addresses of an employee and manager.

but in the alert history it is showing email address correctly, but user is not getting email.

Content (please ensure you mask any confidential information):

Version (include the version you are using, if applicable):

23D

Code Snippet (add any code snippets that support your topic, if applicable):