When Jira projects are created, its outgoing notifications email address is always jira@instancename.atlassian.net. There is no global setting to change this - updating a project's outgoing mail handler has to be done manually and on a per-project basis.

It would be useful to have a global setting to set a custom email address as default for outgoing notifications. Whenever a new project is created, it would already have a custom email address on its Notifications settings.