Setup sendmail in RHEL 5.3 to use external SMTP

I am trying to setup sendmail in Red Hat Enterprise Linux to use an external SMTP. I have followed this steps:

1. Uncomment and change this line in /etc/mail/ as:
define(`SMART_HOST', `mailhost')

2. Add this line to /etc/hosts     mailhost

3. Compile settings
m4 /etc/mail/ > /etc/mail/

4. Restart sendmail service
service sendmail restart

Mail is not being delivered and I cannot figure out why. I have manually tested the external SMTP (using telnet mailhost 25, ..., rcpt to:...) and it works. So I am stuck at this point.

Could you please help me out with this one?

Any help would be very appreciated.
Who is Participating?
Jan SpringerConnect With a Mentor Commented:
The syntax uses a fully qualified domain name.  The DNS server that this machine is using should be able to resolve the FQDN into that IP:

From the Linux machine, what do you get when you type (substituting the domain name):



And then:

    make -C /etc/mail
    service sendmail reload

Have you tried to put brackets around the mailhost?


Open in new window


Regards, Tobias
Also, the IP isn't a valid external IP, but that depends on how you define "external". It's not a routable IP on the internet.

Regards, Tobias
Never miss a deadline with

The revolutionary project management tool is here!   Plan visually with a single glance and make sure your projects get done.

k3paAuthor Commented:
I've tried to use this one:

But nothing happens. The IP associated to mailhost is indeed within our private network but it's accesible. I don't have any trouble when sending mail throught it from the sendmail host.

Please find below the output from /var/log/maillog:

Mar 10 09:15:24 rhelserver sendmail[13482]: p2A8CKYx013482: from=root, size=56, class=0, nrcpts=1, msgid=<201103100812.p2A8CKYx013482@rhelserver.>, relay=root@localhost
Mar 10 09:15:24 rhelserver sendmail[13482]: p2A8CKYx013482:, delay=00:03:04, mailer=esmtp, pri=30056, dsn=4.4.3, stat=queued
k3paAuthor Commented:
The host is not being resolved. Although the SMTP is whithin our corporate network, it's no so easy to add record to it because of the bureaucracy involved.

I will try to set up a local dns server to target the smtp server.
You can try to add the "mailhost" host to the local /etc/hosts file.

Regards, Tobias
k3paConnect With a Mentor Author Commented:
I set up a dns server and names are being resolved ok.

> host has has address

I also tested MX record:

> nslookup -query="MX"
Address:  mail exchanger = 10

I changed like this:

However, emails are not sent. :(

Where shoud I do next?
Can you see anything in the logs to help understand what's wrong?

Regards, Tobias
k3paAuthor Commented:
Wow it's working now.

Setting up a DNS server with the MX host has worked. It's important to note that I am using the default file. I will have to use this solution because I don't want to spend more time with this issue.

Thank you for your support.
k3paAuthor Commented:
Fully qualified names and setting up a custom DNS server solved the issue.
All Courses

From novice to tech pro — start learning today.