Fedora sendmail setup. Tips for hosts/domains and masquerading.

Notes on my fedora sendmail setup.  I have had my fedora linux server setup for a couple of years with no email —  on purpose, to avoid spam hassles.  But to help my blog work better with plugins I decided to get this machine running sendmail.

I’ve done fedora sendmail setup before on another one of my servers, but it had been so long, I had to start from scratch.  I started by finding a good general setup guide.  This one on the fedora wiki was most worthy.

So the instructions were pretty straight forward.  Since I own my domain name and have a static IP address, the setup is easy.  So I followed the instructions and, well, it didn’t work. My first problem:

Fedora Sendmail setup emails bounced, because email is from [email protected]

So my first couple of test emails sent to my web account bounced back to me, they looked like this:

----- Transcript of session follows -----
... while talking to mx0.gmx.com.:
>>> MAIL From:<[email protected]> SIZE=665
<<< 550 5.1.8 Cannot resolve your domain {mx-us004}
554 5.0.0 Service unavailable

So I had to figure out why my server was putting [email protected]  I learned that my /etc/hosts file was setup wrong.  There’s lots of fedora tips on how to setup your hosts file (here’s a related posting), mine was setup wrong.  One tip, use the sendmail diagnostic tool, as follows:

# sendmail -d0.1 -bv root
 SYSTEM IDENTITY (after readcf) (short domain name) $w = myserver
(canonical domain name) $j = myserver.mydomain.net
       (subdomain name) $m = mydomain.net
            (node name) $k = myserver.mydomain.net

The above is good. Before I debugged my localhost problems, this command showed localhost in each of the domain name lines.  Also, for debugging, I recommend using the mail -vv (two v’s) command line option.  It’s easier than looking in the /var/log/maillog file.

Next problem: the emails were addressed [email protected]

The emails were working, but the From line should say [email protected]  I had to relearn how sendmail masquerading worked.  I had to setup the key parameters in the sendmail.mc file, as follows:


But the masquerading wasn’t working.  When I went to the official sendmail man page for masquerade, it talked about the EXPOSED_USER option.  By default, sendmail assumes the root user never wants to be masqueraded.  Of course, I was troubleshooting my sendmail setup from the root login, so this option had me thinking something was wrong.  I turned of this option, and finally my fedorda sendmail setup was finished.  It took way longer than I thought it would and I felt it was worth writing up.

For reference, here’s what I changed in my sendmail.mc file:

define(`confLOG_LEVEL', `9')dnl
dnl EXPOSED_USER(`root')dnl

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