I'm running multiple websites on a single server. I'm using sendgrid to send my email.
Right now, I have postfix relay all outgoing mail to a single sendgrid account, using smtp_sasl for authentication.
I need to be able to send each domain's email to a different sendgrid account. So, for domain1.com, I'd want to relay to sendgrid using one account, and for domain2.com, I'd need postfix to use a different account to authenticate.