Subdomains...ya feel my pain?

Edit Subject

I have setup sendgrid successfully for my main ecommerce site on mysite.com. However, I also have affiliates.mysite.com, and would like to use sendgrid for outgoing affiliate notifications. So, my affiliate platform is on affiliates.mysite.com, but emails sent from here use the affiliates@mysite.com email address. Can I use my existing sendgrid account from mysite.com to send emails from affiliates@mysite.com, originating from my affiliates.mysite.com subdomain?

Thanks!