Dedicated sendmail email delivery server

[bclark4444]

Scenario: I have a client that has migrated their email to Google Apps and now is using Googles MX servers for incoming email to their domain. Part of their application sends out emails daily (about 27,000 of them) and, unfortunately, Google doesnt allow that many to be sent out from its servers. This becomes an issue because some spam filters apparently check MX records for the senders domain to make sure the email isnt spoofed, so we cant send the emails directly from their application without relaying it through a "legit" email server.

Possible solution: Can i configure an inhouse linux server using sendmail as a delivery agent, allow relaying from the application server, add an MX record pointing to it, and have it only accept incoming emails for my clients domains but relay them to Google. Ill add the MX record with low priority to minimize the chance of it receiving any incoming, but it could still happen.

Is my solution feasible? Or would another approach work better? Any suggestions or advise is welcome.


Thanks
--Brett

BTW: although im very familiar with Linux, sendmail is still a blind-spot for me. I have very little working knowledge of it.

[Mudgen]

Definitely feasible with sendmail. Have done and am doing similar. You can configure sendmail not to accept incoming, if you like, but if your bounces bounce, you'll find yourself blacklisted. You can readily alias any incoming address to /dev/null in /etc/aliases. Lots of other configuration options available to help with quirks/issues you encounter.

Start with a test instance. Ask more questions as you go along if you like. I've been a sendmail practitioner since right after it started replacing MMDF. You could also do it with Postfix, and there's probably help here for that, too.

[rust710]

While configuring sendmail or exim to do what you want, you don't actually have to setup an incoming server. If the spam filter is only matching MX records, then add the MX record, but keep the port closed on the firewall. This is actually a method sometimes used to block spam(some spam generators try low priority MXs first since they occasionally have less spam filters).

If you do decide to configure an incoming server as you mentioned, be sure that the server actually checks the email address is valid. I know exim offers several ways to do this, via a database(MySQL), authentication system(MS AD, NIS, LDAP, etc), or flat file. I don't use sendmail but I would think it would offer at least some of the same. At any rate I recommend this because the gmail server will reject invalid email addresses which will then require your server to generate a bounce message. Infact any message gmail rejects will require your server to generate a bounce message.

Hope that helps

[bclark4444]

Maybe i could ask for additional clarification on an assumption that i was making. Would my delivery box need an MX record to avoid being counted as SPAM, or would an A record suffice as proof that its coming from a legit box? I was told before that someone thought it needed an MX but i have also read online where someone suggested an A record would do. Im not up to speed on how SPAM filtering works so im relying on smarter folks to help me on this one.

Thanks
--Brett

[rust710]

I think your actually looking in the wrong place. I've never encountered a spam filter that checks MX records, and it my be considered improper behavior if it did. If I where to guess I would say it's more likely your mail is being rejected because the ip address is blacklisted, or marked as being a consumer connection. Most cable and dsl connections are marked like this.

You may have more luck relaying through your ISPs mail server.

[asmar]

Are you sure that those 27000 emails are legitimate and all users are subscribed? If yes, the best is to send them over a newsletter application like phplist (see http://phplist.org).
Phplist will help you a lot as you will see all bounce emails and then you can clear your list from faulty emails. You can also limit the outgoing emails per hour.
You will need a dedicated server for that amount of emails and must be properly setup to avoid getting blacklisted or a VPS which is cheaper.

I did a work in the past for a client (large eshop) with 90000 users in his database with daily newsletters and phplist save me huge amount of time.

Regarding your setup, it will be most of the times handles as spam if you've got no reverse DNS and this is something that local servers can't do, you will need a dedicated server/vps on a hosting provider and ofcourse a MX record and a properly configured DNS is a must.