This tech doc explains what Service Desk admins should do to address the issue that occasionally maileater creates tickets in "wrong" tenant.
Release : 17.3
Maileater creates tickets according to the email address of the sender...maileater searches for contact in the user repository who has the sender's email address and assign the ticket tenant according to that.
However, if multiple users in different tenants share the same email address, maileater sometimes won't be able to figure out the "right" user therefore you may see the ticket is assigned to "wrong" tenant.
To avoid situation like this, Service Desk admin would need to make sure no two users, in the same tenant or not, share the same email address.
If you think this best practice should be mandatory enforced, please submit an idea/enhancement request from community web site