I think it would be a pretty good enhancement to offer mailboxes to our invoice and order-confirmation customers.
Benefits for us:
The customer does not have to worry about accessing Mailboxes
We have a good advertisement! thousands of vendors would get to know the name doxis or SER.
PS saves a lot of troubles: accessing the customers Mail Servers can be a huge pain which eats the projects budget (I can tell you some of the troubles, if interested)
we would be the "all-in-one" provider for our customers
I think this offer would perfectly fit the smaller size customers who are interested in our business tier licenses.
I would offer it only for our cloud customers. Not for on-premise installations.