目的

On occasion, there may be a need for a Jira Administrator to notify users of any event that will be happening on the site. For example, maintenance notification, rebuilding index, upgrade or even a planned outage.

ソリューション

1. Use Jira's Send E-mail feature. 
   To access this feature, you need to have Jira Administrator global permission on the site.
   Navigate to > System > Mail > Send E-mail page, and you can draft a message to the list of Groups or Project Roles you want to send the email to
   

2. (Server and Data Center only) In the event of a Jira outage and you would like to send a notification email to all the users, you can retrieve the list of emails through Jira database:

    SELECT DISTINCT email_address FROM cwd_user;

   You can then send the email to the list of addresses generated from that query.  However, If you wish to fetch all the user and their email addresses based on the application (Jira Core, Jira Software, Jira Service Management), you may refer the document Get list of licensed users in Jira server 

3. (Server and Data Center only) Alternatively, you can use the Announcement Banner to inform any information or activity happening in the instance: Configuring an Announcement Banner