how do I conceptualize system & virtual users?

[lejeczek]

On 19/06/15 15:13, Mauricio Tavares wrote:
> On Jun 19, 2015 9:08 AM, "lejeczek" <peljasz at yahoo.co.uk> wrote:
>> I guess this would be a common case, I am hoping for some final
> clarification.
>> a few Linux boxes share ldap (multi-master) backend that PAM/SSSD uses to
> authenticated users, and these LDAPs are also is used by Samba, users start
> @ uid 1000.
>> Boxes are in the same both DNS and Samba domains.
>>
>> Do I treat these users as system or virtual users from postfix/dovecot
> perspective?
>> If it can be a matter of choice then which is better/best?
>>
>        I would make them virtual users. This way you can abstract and scale
> things up. Also your normal users then would not need to have access to
> your mail servers; they only access the services.
>
>> many thanks.
it can be a tricky for beginner to define those, in old days 
when one said system users thought of OS dedicated accounts 
for daemons/services etc.
In this team of postfix+dovecot, which one decides whether 
user is canonical/system or virtual?