ActionMailer for bulk emails

I am using Postfix as my mail handler. When I have ActionMailer deliver
a large number of emails, it takes a while. It seems that in my Rails
process, ActionMailer waits for Postfix to actually send each message
before returning and moving on. Is there a way to configure either
ActionMailer or Postfix to speed the sending of bulk mails, perhaps by
having ActionMailer just submit the mail to a queue instead of waiting
for the mail to actually be sent?

thanks,
Jeff