I want to host my own mail server and in order to do so I've installed Postfix 2.7.0 and Dovecot 1.2.9 on Ubuntu Server 10.04.

One big problem I face right now is that Google SMTP servers reject my mail ONLY WHEN it is being sent remotely. Strange, right?

So if I telnet localhost 25, then issue AUTH LOGIN (not an open relay of course) then send the mail I get a status = sent and I actually receive the mail message in my Gmail's account Inbox. Works like a charm.

On the other hand, if I want to send the mail from a remote host, I use:

Then I issue AUTH LOGIN, the login process is successful. So I don't have a problem communicating with my server. I can see what happens in the log files. But when I try to send mail like this, Google replies:

Why Google accepts my mail if being sent locally but rejects it when I openssl to my server and send it remotely?

It's like Postfix on my server makes Google aware of how email got to it in the first place and this way enables Google to reject mail that was not sent locally.

Check your NDR messages to see what SMTP error is being returned. Most likely the DNS information on your mail headers aren't returning a valid address when Google runs the messages through their spam filter.

OK, but I use the same mail server to send mail in both cases.

The only difference is that in

Case 1: I issue the commands from my mail server terminal itself.
Case 2: I send the mail by issuing an openssl s_client -connect to my mail server, with successful authentication.

Why doesn't Google reject my mail in both cases then? Mail headers should be the same.

Because google thinks that mail from <spammer.ip> is still spam, even if it is routed via <clean.server>

OK, in this case, considering that I am using Postfix SASL, so I do authenticate as a valid user from my mail server point of view(which is clean), is there a way to make my mail server hide the original address that mail is actually coming from? Could I impersonate my server?

I mean, this shouldn't be unethical as I do provide some kind of authentication before I ask for mail relay service from my server.

Finally solved after hundreds of hours of pain:

Google SMTP rejected my mail because Postfix failed to automatically generate a Message-ID for mail that it was relaying.
Strange enough, this didn't happen if mail was sent locally(telnet localhost 25) - so Postfix was generating Message IDs for these.

So the solution was to add
in /etc/postfix/main.cf.

Hope someone else will not have to struggle with this for so long.

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