I have one Organization in Jira Service desk in which all the customers have stopped receiving notification emails. This recently happened, within the past three months.
The customer can create requests by the portal and by sending an email. They can also log into the portal and review their issues as well.
The problem is that they do not receive any email notifications of changes. They are the only organization that this is happening to. We review their email white-list and have confirmed that atlassian is white-listed.
Since this is the only organization, we're pretty sure that it has something to do on their side with spam filters, but can't figure where to look next.