Hi There!
We have a customer with many users that usually open issues with us, and only one of them can not receive mail notifications from Jira Service Desk. He can send a mail and open an issue on Jira SD, but he is not receiving mail notifications after that.
It was checked with his IT team, and there is no blocks on their firewall, or in the mail service on his PC/Laptop. We asked him to include our mailer on his trusted mail list, but no sucessfull.