regulate mail flow by domain

[François Yuul]

Hello,
 
I use Postfix as a relay SMTP to send bulk mail (newsletter).
 
And I would like to regulate them according to the domain name of the recipient.
 
For example, if I have to send 100 emails to domainA and 100 mails to domainB
 
I would like Postfix regulate those mails by sending in a first time 50 emails 
to domainA and 50 emails to domainB then in a second time 50 mails to domainA 
and 50 emails to
 
domainB.
 
Is there a solution to my problem?
 
Thank you for your answers.