I am in the process of setting up a mail server (using sendmail to be exact). The server needs to be as open towards receiving notifications of "bad"/bouncing emails as entirely possible.
I am not exactly into the nitty gritty details of how this entire bouncing/bad email thing works, so I am not sure exactly how much I need to do to make this work.
Currently if I try to send an email to an email address on a domain hosted within Google Apps I get a notification in return just fine. However as there's no ports open on the server sending the emails out, I am thinking there could be some problems if the email is bounced further out the process?
Does anyone know how to best achieve this? Is this as simple as opening a port? Or are there other things that needs to be taken into consideration?
Any pointers / links to resources would be greatly appreciated. I am not a system administrator - but unfortunately the company I work for do not have any, so someone has to play the role.
EDIT: As stated, the type of system needed to be expanded on: The server is a debian lenny system, sendmail is installed through the official repositories (through "apt-get install...") - everything else is left to the stock configs.