How can I configure postfix smtp per user?

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http://unix.stackexchange.com – I have previously used msmtp as my MDA. msmtp has a configuration file with username and password of the outgoing smtp server (eg gmail) stored in my home directory. I've recently changed distributions to CentOS 6.3 for reasons of support (only supported distribution for third party software). I tried to install msmtp but it wasn't available in any of the repositories. I finally got an rpm from fedora and installed that but it still doesn't work (can't find ca-certificates). So I decided I'd try with Postfix as it's the default on RHEL. What I'm trying to do is set up sendmail (git and mutt) (HowTos)