Explanation
The newaliases command is a Postfix command that can be used to rebuild all of the alias database files with a single invocation and without the need for any command line arguments. The newaliases command is equivalent to running the postalias command on each file specified by the alias_database parameter in the Postfix main.cf configuration file. The newaliases command reads the text files that contain the alias definitions and creates the indexed files in dbm or db format that are used for fast lookup by the mail system.
The newaliases command should be executed whenever the alias database is changed, in order to update the indexed files. For example:
newaliases
The other commands are not equivalent to the newaliases command. The makealiases command is not a valid Postfix command. The postalias command can be used to rebuild a single alias database file, but it requires the file name as an argument. The postmapbuild command is not a valid Postfix command.
References:
LPIC-2 Exam 202 Objectives, Objective 205.3: Managing a postfix server
Postfix Basic Configuration, Postfix Documentation
Postfix manual - aliases(5), Postfix Documentation
Postfix manual - newaliases(1), Postfix Documentation
Postfix manual - postalias(1), Postfix Documentation