I'm running redhat7.1 and want to send outgoing mail only. It was working fine (test 1 address) and now I'm using regularly and 8 of 10 mails bounce. I know the setup must be screwed up. It appears to be a dns issue but I haven't a clue which file to change.

Heres an error transcript:

----- Transcript of session follows -----
... while talking to mailin-03.mx.aol.com.:
>>> MAIL From:<apache@localhost.localdomain>
<<< 550 REQUESTED ACTION NOT TAKEN: DNS FAILURE
554 5.0.0 DBKCK38@AOL.COM... Service unavailable

--g0IJEib26357.1011381311/localhost.localdomain
Content-Type: message/delivery-status

Reporting-MTA: dns; localhost.localdomain
Arrival-Date: Fri, 18 Jan 2002 13:58:13 -0500

Final-Recipient: RFC822; DBKCK38@AOL.COM
Action: failed
Status: 5.0.0
Diagnostic-Code: SMTP; 550 REQUESTED ACTION NOT TAKEN: DNS FAILURE
Last-Attempt-Date: Fri, 18 Jan 2002 14:15:11 -0500

--g0IJEib26357.1011381311/localhost.localdomain
Content-Type: message/rfc822

Return-Path: <apache>
Received: (from apache@localhost)
by localhost.localdomain (8.11.2/8.11.2) id g0IIwD326228;
Fri, 18 Jan 2002 13:58:13 -0500
Date: Fri, 18 Jan 2002 13:58:13 -0500
Message-Id: <200201181858.g0IIwD326228@localhost.localdomain>
From: the_dit@hotmail.com
To: DBKCK38@AOL.COM
Subject: ...

--g0IJEib26357.1011381311/localhost.localdomain--

Are 8 out of 10 e-mails going to AOL?

There's the problem. the aol.com smtp server checked to see who was sending it. localhost.localdomain was sending, which is not a valid fully qualified domain name (it is fully qualified, just not valid on the Internet as it's not routable).

What you need to do is configure sendmail to it uses your system's fully qualified domain name (mydomain.org or mysubnet.mydomain.org).

Edit the sendmail.cf file (/etc/mail/sendmail.cf in most installations, sometimes /etc/sendmail.cf or /usr/lib/sendmail.cf) and see if there's a line staring with Dj. If not, add it as follows:

Djmydomain.org

or

Djmysubnet.mydomain.org

Restart sendmail and try again.

btw you're kind of lucky that 2 out of those 10 went through. That's indication of a poorly setup smtp server somewhere. No server should allow a localhost.localdomain envelope as it should only be used on LAN (and even there it's not advisable since every PC has that setup as the FQDN for 127.0.0.1). But now we're getting into network setup, kinda off topic here.

I've added the Dj line and have a queation about the my.domain.net assignment.

My registered domain is tecsol.org, do I use www.tecsol.org or just tecsol.org?

Also does tecsol have to be referenced on my server somewhere? if so can you give me the location and format.

Finally, my ip points to a router which redirects to my internal server. Would that be a problem.

thanks.

I'd use tecsol.org

Make sure that in the DNS of tecsol.org you have tecsol.org. listed in the MX record. Right now it doesn't look like you have added an MX (mail exchanger) record to your DNS server.

Secondly, a lot of servers will do a check on you, kind of like this:

your sendmail sends an email and will identify as:
HELO <here what you listed at the Dj option>

Now, the remote site will first check our IP address, and do a reverse lookup on it to make sure the hostname you entered at Dj and the IP resolve back and forth to the same thing.

You said something about a router who directs traffic from an ip to internal server. I don't have much exeprience doing that. I'd setup the router machine to be the mailserver too. then again if you use ip_masquerading it may work just fine. Just make sure the hostname your sendmail will report has a valid IP address and that it's IP address resolves back into that hostname you entered.

I'm a newbie to all of this. No idea how to setup an MX record or masquerade. I think Sendmail.org's docs are the worst I've seen on the net. Seems to be an assumption you're already very adept with sendmail.

thanks

sendmail docs are bad yes. You'll be better off buying the "Sendmail" book published by O'Reilly. It'll even give you a nice theory rundown of how SMTP works, how servers interact, what kind of verification tests they run, etc.

I may be adept with Sendmail but that only made me dislike sendmail (the more i know about it, the less I liked it). I wouldn't touch sendmail with a 10 foot pole whenever I have a say. I'm using postfix (www.postfix.org) now and have never been happier. It's a lot better in many ways (one important way it's a lot more secure than sendmail).

Back to the question. Don't worry about masquerading. Your router is already doing it if you need it (else you'd know and would have set it up yourself). About MX: you'll have to update the DNS records for your domain and add it. Perhaps your registrar does DNS for you and you can login in their control panel and add a mail exchange record (it's simply the hostname of the machine that does your email)