Problem Definition

Customers who have configured Jira to send Emails on behalf of their Domains notice that the Service Desk Customer Invitations still send as jira (at) instance.atlassian.net

Suggested Solution

If the Service Desk Project has been configured to Send on Behalf of the Customer's Domain, the invitation should come from that address
It appears that the "Send on Behalf" Email Address is only used for Jira and Service Desk Notifications and not for Customer Invitations to a Project.

Service Desk Notification:

Invitation:

Why this is important

A Customer's Customer may have mail filtering or may not trust the jira (at) instance.atlassian.net email

Workaround

The jira (at) instance.atlassian.net email address should be whitelisted to ensure mail delivery from the instance