Choose single domain or multiple domains.
When using the single domain, each account created will be the first part of the mail address or the "uid" you have set in each member.
For most cases, this member management structure can be used on a single organization.
The main problem is when you want to create the same member name in other organizations.
For example a member called "support" cannot be stored on several organization because the uid cannot be the same.
To resolve this issue you can switch the whole server to multiple domains.
In a "multiple organization" mode, each account must use the eMail address as the login credential.
in this case a member called "support" in a multiple organization mode should be email@example.com and firstname.lastname@example.org as the main uid.
Note: it is mandatory to choose this mode at the begin of the installation server just before creating members: Switching from single mode to multiple mode require to remove all members/Mailboxes and re-create them.
Switch to multiple domains:
On the Mailbox section, under the status area, click on "Multi-domains" icon.
- Turn to green the red circle and click on apply button.