How to Fix “Unable to Qualify My Own Domain Name” Error in Sendmail Configuration


2 views

When Sendmail logs the message unable to qualify my own domain name (myhost) -- using short name, it indicates the mail transfer agent can't properly resolve your server's fully qualified domain name (FQDN). This commonly occurs when:

  • Your hostname isn't properly mapped in DNS
  • The /etc/hosts file lacks proper entries
  • Domain search paths aren't configured correctly

Your current /etc/hosts configuration shows:

127.0.0.1   localhost myhost.mydomain.eu myhost.domain2.eu localhost.localdomain
127.0.1.1   myhost

The issue stems from Sendmail not finding a matching FQDN for the short hostname myhost in your second line.

Solution 1: Modify /etc/hosts (Recommended)
Update your hosts file to ensure proper FQDN mapping:

127.0.0.1   localhost localhost.localdomain
192.168.1.100 myhost.mydomain.eu myhost

Key points:

  • Replace 192.168.1.100 with your actual server IP
  • Place the FQDN first, then the short name
  • Ensure reverse DNS matches this configuration

Solution 2: Configure Sendmail Directly
Edit /etc/mail/sendmail.mc and add:

define(confDOMAIN_NAME', myhost.mydomain.eu')dnl
define(confCF_VERSION', myhost.mydomain.eu')dnl

Then rebuild the configuration:

m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf
service sendmail restart

After making changes, verify with:

hostname -f  # Should return FQDN
sendmail -d0.1 -bv root | grep Canonical  # Check Sendmail name resolution
dig -x your.server.ip  # Verify reverse DNS

If issues persist, check:

/etc/host.conf
/etc/nsswitch.conf
/etc/resolv.conf

Ensure these files contain proper search domains and host resolution order (typically files dns).

For a server with multiple domains:

# /etc/hosts
192.168.1.100 mail.mydomain.com mail mail-backup.mydomain.net

# /etc/mail/sendmail.mc
define(confDOMAIN_NAME', mail.mydomain.com')dnl
define(confDONT_PROBE_INTERFACES', true')dnl

When Sendmail complains about being "unable to qualify my own domain name," it's indicating a fundamental DNS resolution problem. The mail transfer agent (MTA) can't properly map your server's hostname to a fully qualified domain name (FQDN).

Your current /etc/hosts configuration shows:

127.0.0.1   localhost myhost.mydomain.eu myhost.domain2.eu localhost.localdomain
127.0.1.1   myhost

The key issue here is that myhost appears without a domain qualification on the second line. Sendmail expects every host reference to be fully qualified.

Here's the correct way to structure your hosts file for Sendmail:

127.0.0.1   localhost localhost.localdomain
192.168.1.100  myhost.mydomain.eu myhost

Key requirements:

  • Each host must have exactly one FQDN entry
  • The short name should appear after the FQDN
  • Never use 127.0.1.1 for your primary hostname

Verify and set your hostname properly:

# Check current hostname
hostname
hostname -f

# Set FQDN permanently (Debian/Ubuntu)
echo "myhost.mydomain.eu" > /etc/hostname
hostnamectl set-hostname myhost.mydomain.eu

# For CentOS/RHEL
echo "HOSTNAME=myhost.mydomain.eu" >> /etc/sysconfig/network

Add these to your /etc/mail/sendmail.mc:

define(confDOMAIN_NAME', mydomain.eu')dnl
define(confCF_VERSION', myhost.mydomain.eu')dnl

Then regenerate your Sendmail configuration:

make -C /etc/mail
systemctl restart sendmail

Test your configuration with these commands:

# Verify forward resolution
host myhost.mydomain.eu

# Check reverse DNS
host 192.168.1.100

# Sendmail test mode
sendmail -bv root

For production systems, consider proper DNS setup:

# Example BIND zone entry
myhost    IN    A    192.168.1.100
100.1.168.192.in-addr.arpa. IN PTR myhost.mydomain.eu.

Remember to update your /etc/nsswitch.conf to prioritize DNS:

hosts: files dns