To answer your second question, the name "default identity" cannot be changed (as far as I know).

You can, however, change the command line that runs Pegasus so that it starts up with one of your custom, named identities. See the help file page about command line options.

1, When Pmail installed, the admin user name create by software automatically? Want to change to my own prefer name, is it possible?

2, The default identity is also created by Pmail. Would like to change it as well. Possible? 

If you have set up as a single user you might have to do it in stages.

Back up yur Mail directory.

In Addresses - User management, set up a new user with administrator status, not using the name you want (ultimately) to become.

Open Pmail as that user and change Admin to the user name you want.

Open Pmail as that user and delete the interim user.

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James Quigley