What is the Difference between Sender Adress and Alias

With a Standard or Professional Account, Alias addresses can be defined. These are additional swissmail.org email addresses, but belong to the same account and are freely selectable. Messages sent to such aliases will automatically be forwarded to the mailbox they belong to, i.e. to the primary address.

With a Standard or Professional Account additional Sender addresses which do not belong to swissmail.org can be defined. You have to be the owner of those email addresses as they only are active when the owner confirms them (a confirmation link will be sent to the owner). The sender addresses can only be used as a sender.