Jira Service Desk does not appear to have a method to email all Customers at once, short of using the internal How to send an email to all Jira users. You would need to gather a list of emails of all Customers and send using this method, which isn't very convenient.
Provide a method in Jira Service Desk to send a single email out to all Customers
Soon we will be merging 2 JSD instances into 1. We need to do comms out to our user base on both JSD's of the upcoming merge and the short outage on the cutover day.
We have added announcements on the Service Desks affected which is fine for users who visit in the week before the merge.
However I would feel more re-assured if I was able to mail all customers from the Customers section of JSD to reach more customers before the outage. But I can't find any option to email all customers? Or even export all customer email addresses out to csv which would be a workaround.