Confluence has been updated to version 6.15.9


You have setup the exalate notifications in your node, but no notifications are sent.  


Currently mimecast (and maybe other mailservers) are bouncing mails from due to an unknown reason.
Please make sure that mails from are not being bounced.


Configure 'the permitted senders' option on your mailserver.
In the case of mimecast - check following document