We are a hosting provider and provide SMTP relay functionality for our customer. Because relaying mail can cause blacklisting in some cases, we have a separate relay for each customer each with it's own outbound IP address. In case a single customer sends out spam (willing or unwilling), only that IP will be blacklisted and other relay customers won't be affected.
This solution requires us to have separate servers for each and every customer, which is from an administrative point of view not very efficient.
I'm looking for an SMTP relay solution that can choose the source IP address based on the sender of the email, so I can consolidate all current relays into one.
Is it possible to do this with the hub transport or edge transport role? Or is anyone aware of another product that is able to do this?