Problem with saslauthd on every new installation

Greetings everybody.

We are facing the exact same error on every new installation the last days. We use KVM virtualization, and install Virtualmin on Centos 7.

When setting up a virtual server and trying to connect to a user the following error shows up and connection is not possible.

saslauthd[7003]: DEBUG: auth_pam: pam_authenticate failed: User not known to the underlying authentication module
saslauthd[7003]: do_auth : auth failure: [user=mboziki] [service=smtp] [] [mech=pam] [reason=PAM auth error]
saslauthd[6999]: pam_unix(smtp:auth): check pass; user unknown
saslauthd[6999]: pam_unix(smtp:auth): authentication failure; logname= uid=0 euid=0 tty= ruser= rhost=

I am aware that putting an -r argument on FLAGS on file /etc/sysconfig/saslauthd fixes the problem but I would like to know if there is an solution to prevent this from happening(whether I am doing something wrong).