Hello all!

I'm a newbie and recently purchased Red Hat Linux 9 (and also the Red Hat Linux 9 Bible).

The Apache web server works well, however I'm experiencing difficulties with the Send Mail mail server. Sending and receiving email to internal users works well, but I'm not able to receive external email.

The return mail error is:
TCP active open: Failed connect() Error: Connection refused

Is anyone else familiar with this error, or how to resolve it?

Thanks in advance!

Douglazb

You might have a firewall or packet filter (iptables) installed without having
punched the holes to allow incoming SMTP traffic. Back up your config file
/etc/sysconfig/iptables and have a look at
redhat-config-securitylevel , but be careful with it.
My version on RH 8.0 does not remember previous settings.
You also can try to run tcpdump -i eth0
to see what happens on the network.

While you may also be having a firewall problem as stonux suggests, Sendmail by default only accepts email from local users (on the localhost or lo interface). To change this, you will want to do the following as root:

1) BACK UP the contents of /etc/mail... just in case =
2) Edit /etc/mail/sendmail.mc
a) Look for a line that looks like this:

DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl

b) Add dnl (which stands for 'do not load') to the beginning of the line so it looks like:

dnl DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl

3) Run the command 'm4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf'
4) Run 'service sendmail restart'

Notes:
If you get an error during step number 3 about not being able to find sendmail-cf or something to that effect, install the sendmail-cf rpm off of your RedHat CDs or run 'up2date sendmail-cf' if you have up2date set up.

Here's what those instructions have you do -- The config file that sendmail actually uses is called /etc/mail/sendmail.cf, but the syntax for that file is... wierd, to say the least. To avoid having to modify it by hand, the file /etc/mail/sendmail.mc is provided. This file is written in a special macro language called m4, which is supposedly easier to read and modify than the original sendmail.cf. When you run the contents of sendmail.mc through the m4 interpreter (step 3) it interprets those macros and produces a sendmail.cf file. Normally it would spit the new file's contents out to the sceen, but the '> /etc/mail/sendmail.cf' redirects it into a file instead. The modification you made to sendmail.mc and then translated into a new sendmail.cf simply tells sendmail to ignore the line that would normally instruct it to only listen on the local interface. When you restart sendmail (step 4) it re-reads your new sendmail.cf and should accept mail from anyone.

If you're going to run sendmail, do make sure you've got it all up2dated so that you're using all relevant security patches and set up a firewall unless you really do intend for *everyone* to be able to access this service.

Have fun.

To stonux: I'm not familiar with the iptables. The router is the firewall and I used port forwarding to direct request for port 80 (http traffic), port 25 (smtp), and port 110 (for pop). Can someone confirm these are the 3 ports that need forwarded to the computer with linux server installed?

To usernamenumber: Excellent information, however the line you referenced had already been dnl and compiled successfully.

Could the error be caused by my ISP, controlling the ip's redirected through DynDNS.org? How can I confirm with port 25 is blocked by my ISP? Any other ideas?

Thanks in advance!
Douglas

iptables acts like a firewall on your linux machine. If you already have a firewall in your router, you can disable iptables and look if SMTP gets through.

It is very common for ISPs to block connections to low (ie service) ports on their customers' machines. As for ways to find out if its being blocked...

I think the best way would be to call your ISP and ask. They'll probably tell you that you have to buy a business account. If they say they don't filter then you should continue troubleshooting sendmail.

--Brad

try tcpdump -i eth0 to see whether the SMTP packets come in.
as you have opened port 80 for HTTP, check if you get your web server's test page.
I also heard about ISPs forcing an SMTP relay through them for offering antivirus and antispam services.

sorry: you said http is OK, and I already suggested tcpdump.