Take the 2-minute tour ×  I wish to host some managed email
servers for some customers. Each customer will have their own
email server which will be an all-in-one virtual machine running
postfix, dovecot and some webmail suite.  Even though each
customer will have their own server, I do not wish to give each
email server it's own public facing IP. I wish to avail the use
of proxy servers so all customers use the same public IP. As for
the "smtp-in" from the public internet, this isn't a problem as
I can set up many mx servers (using postfix) which will store-
and-forward the mail to the correct server (using transport
maps). As for the IMAP access from the customer, I was thinking
of using perdition which is an IMAP proxy - I believe that this
will suit my needs.  I am confused however on what to use for
the "smtp-out" proxy. The customers will have to authenticate
with their receptive email server, however they will have to go
via a proxy of some sort as they won't have direct access to
their server instance.