Normally, all system users can be reached in one domain. This can be disabled under Services > Email > Domains : Settings. In doing so, only the addresses that are explicitly specified are valid within a domain.
It is also possible to specify that emails to unknown recipients in this domain are not blocked ("550 User unknown"), but forwarded to the postmaster.
Each user can be reached under their username in all domains where the "All system users valid" option is active. In addition, aliases with which the user can also be accessed can be set up for each user under Usermanager > User : Addresses.
The aliases, like normal names, can be valid for all domains or only for a specific domain. This makes it possible, for example, to forward the address "Info" for multiple domains to different users.
If an address is entered for "", this means that it is valid for all domains where the "All system users reachable" option is active.
It is also possible to enter aliases for external domains. This may be necessary for an automatic response (see Section 14.6.2, “Automatic Response”). In addition, emails to such addresses are delivered locally immediately and do not go through the provider. If no domains are used on a system, but only individual POP accounts, you can save the transfer of internal emails to the provider and back.
A complete name can be entered for each alias. This is used as the sender for webmail.