[PROBLEM] Aliases do not appear in autocomplete

There is an option for each of the aliases which are created under each domain name called "Visible Internally". If this option is not enabled, during composing, the user will not get Autocomplete suggestion for the specific alias name.

To configure this setting, navigate to Domain | Aliases and right click on the alias name that you need to modify and click on Edit Alias. In the dialog box opened, check the Visible Internally checkbox. Click on Save.

Your alias "visible Internally" settings should look as illustrated below: