If you plan to create mailboxes for a subdomain, but it is not in the domain selection list when you create the mailbox, do the following:
To create a mailbox, do the following:
Make sure in the section "My sites
»Added a site with the name of the domain for which the mailbox will be created. If the site is missing, add
Click "Create mailbox
If there are already created mailboxes for the domain, the button will also be available next to them:
Fill in the fields and click "Create mailbox
Check the operation of the created mailbox.