Currently we use a hosting company for our Exchange services. We are considering a switch to Google apps, but that is in a pilot program at the present time.
Our Exchange provider and Google Apps both have the ability to send e-mail that has been addressed to unknown users to another SMTP server.
I'm looking for advice on how I could setup an SMTP server that would allow me to setup the following:
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Allow me to enter a list, or perhaps create a user account for any past employees. Any mail messages sent to the past employee would have a custom response sent back to the sender explaining that this person is no longer at the company and they should re-send their e-mail to person X that is now handling the past employees work.
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Send a NDR bounce message for any other user that is not defined in the system.
We are primarily a Windows shop, but I don't have a problem in setting up a Linux solution to handle this since it will be a fairly low maintenance system. We don't have that many employees come and go 🙂
Also, if we do switch to Google Apps then I would also make this system an outgoing SMTP server to handle sending our outgoing mail from our web apps since Google limits each user account to 2,000 messages a day.
EDIT: I should explain this a little more. Right now, the company that we use for Exchange hosting does not send NDR's. They claim this is to prevent spammers from sending spam to their servers to fake accounts with real, but spoofed, e-mail address in the return path. Thus delivering the spam message to the intended recipient through the NDR mechanism.
By setting up a separate SMTP server that I would control and they would deliver all messages to that did not match a current account, then I can send NDR messages back to the sender.
We have had a problem in the past where someone sent an e-mail to us but had a typo in the address. However, since our provider does not send NDR's back they though the message was delivered, but we never know about the message.
Best Answer
Wouldn't it be easier to just forward the ex-employee's mail to the appropriate CURRENT employee that is now responsible for the ex's tasks?
I would think that an autoresponder and a forward is all you need?
UPDATE:
Your hosting company not sending NDR's is actually a "good idea". Basically what they're trying to prevent is "backscatter". More information about backscatter can be found here:
http://en.wikipedia.org/wiki/Backscatter_(e-mail)
The main problem I see with what you're trying to do (ie. set up your own server) is that you might be better served with a simple auto-responder rather than a whole new server just to send out bounces.
Is there a particular reason why you want to "bounce" the message rather than just tell the sender that the employee is no longer with you?
The next problem is a little more difficult... LEGITIMATE email with typos that don't bounce back. No bounce means no error, right? Unfortunately no. But to get around the problem you really want to look at the problem closer.
YOUR SERVER should NOT be bouncing the message back to the sender. The SENDER's server should be the one bouncing.
For example, the sender sends an email to jon@domain.com instead of john@domain.com. His server then connects to your server. Your server should immediately say "We don't have a user by the name of "jon@domain.com" here. The SENDER'S server should handle the bounce.
The only bounces you should really be concerned with are bouncing back to your own users.
Please note that I have over generalized this A LOT so before I get a ton of replies from people picking holes in this please take that into consideration.
More information about bouncing, spam, backscatter, etc. can be found here:
http://en.wikipedia.org/wiki/Bounce_message
Email and spam is a twisted world. There is no 100% solution right now.
I learned about backscatter the hard way when I client of mine's email server ended up on several blacklists. It seems that the server was being used to backscatter spam all over the place and the (misconfigured) email server was sending out thousands of bounces.
The immediate fix (and the only way to get off the cursed lists) was to just drop the emails silently and do NO BOUNCING.
Later on the server was configured to only bounce to local recipients.
For simplicity sake, bouncing emails is basically just a specialized form of autoresponder. In your situation I think you could easily get away with setting up a simple auto-responder for your ex-employees and then forward the email (or not) depending on the content of your auto-response.
I hope this helps.