I wonder if this might be possible with Sendmail?

When we send out a newsletter to our subscribers, it tends to slow down our regular email from clients on our domain. I have other stand alone servers I could use as MTAs to share the burden when there's a spike in demand. Due to the constraints of our newsletter software and other infrastructure, what I'd like to do is this:

Is it possible to have one Sendmail be the single MTA that the newsletter software talks to and have this server then act as a 'load balancer' or at least a 'round robin', or even 'randomizer' where it relays to, so we can spread the load across 3 other servers that do the actual delivery?

I'd appreciate if anyone knows if this is possible.

thanks....

PS. I really do need to do it this way if possible, due to some other constraints. This is only for outgoing email.