[Exim] Question about vdomain/PAM/SMTPAuth support in 4.20

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is it complicated to set up PAM/SMTPauth/vdomain in exim 4.20, is there a
simple step-by-step instruction list? would it be easier to use PAM or just
use /etc/shadow? will PAM read the /etc/vmail/domain.passwd &
/etc/vmail/domain.shadow for user authentication?

I'm using the virtual domains as set up by linuxconf.

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