We currently use a 3rd party hosted e-mail system using SMTP and IMAP. I was curious is there a way to setup an internal SMTP gateway or server that the internal client can connect through to send/retrieve e-mail to/from the 3rd party? Each client does have to authenticate to the 3rd party to retrieve/send e-mail so it would have to pass credentials on to the 3rd party host.

So in a diagram it would look like this:

Client sends e-mail --> Internal SMTP --> 3rd Party Hoster --> Recipient

Client "retrieve e-mail" --> Internal SMTP --> 3rd Party -- > Internal SMTP --> Client receives new e-mail messages.

The idea is to better log incoming/outgoing messages to track for spam or what not. Currently our firewall does not do this. Upgrade is in process but we all know how IT budgeting goes... We are a virtualized environment so we can run a virtual SMTP.


If you're looking for a turn-key solution, you might want to investigate the contribs.org server, it has an email proxy integrated, and can also be set up as the end point of a relay, I used to configure servers to arrive at a proper MX, then have the transport set up the internal server as the final destination. The only work you will have to do is create the email accounts on the server.

Otherwise, if you want to recreate what it does, you will need to redirect outgoing port 25 traffic to an internal server with your firewall, and have that server configured to send mail outwards. You will also want to set the internal mailserver up as the final destination for your mail. In this manner you can intercept most traffic (SMTPS, POP3S and IMAPS excluded, unless you set them up on your internal server and redirect traffic on those ports there.).

The other option with the retrieval might be something like fetchmail.


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