[CentOS] postfix vurtual user

> 1. what should i do so that the user does not have to fill thier full
> email address (user at domain1.com) at the login page of squirellmail.
> it's moreindly to just put "user" as they used before.

Do you have only one domain? If so, modify squirrelmail php files directly.

> 
> 2. how do i convert all the previous email to the new mailbox format.

Are you using maildir format now?