How does randomize subscribers work?

[theseagull]

Suppose I have 9000 subs in my list which have been added from 1st Jan to 30th Jan

If I mail to 6000 subs and select do not randomize subscribers, does it select the oldest 6K or the newest 6K to send message to?

I understand that randomize sub will send to any 6K at random

 

[laurentiu]

If I mail to 6000 subs and select do not randomize subscribers, does it select the oldest 6K or the newest 6K to send message to?

This depends at query returned by mysql, they will most likely be selected in the order in which they were added.

I understand that randomize sub will send to any 6K at random

That is true.