Mar 3 17:33:09 localdomain authdaemond: authpam: username 'aliasuser@localdomain' not found in password file
The log lines look as if you tried to use the alias to connect to imap, pop3 or smtp-auth. Aliases are no accounts that can be used for authentication, they are just an alias for an existing account. This means you can send emails to this alias, but to fetch the emails from the server or use smtp-auth, you have to use the mail address of the mailbox as username for authentication and not the alias address.
To check if aliases work, do the following:
Login to your server with webmail by using the mailbox and not the alias. Then send from this webmail account a email to the alias email address. You should receive the email in the webamil inbox within 1 minute (takes some time to check the incoming and outgoing email in amavisd).