When configuring a standalone Linux mail server with Postfix, a common roadblock is encountering the bounce message "domain of sender address does not exist." This typically occurs when your server attempts to send emails using a non-FQDN (Fully Qualified Domain Name) like root@domain.local that lacks proper DNS resolution.

The primary solution involves modifying your /etc/postfix/main.cf file to establish proper sender domains. Here's the critical configuration:

# Set your actual internet domain
myorigin = yourdomain.com
mydomain = yourdomain.com

# For systems without permanent internet domains
myhostname = mail.yourdomain.com
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain

# Important for sender validation
smtpd_sender_restrictions = permit_mynetworks, reject_unknown_sender_domain

For a development server that needs to send legitimate emails, you might use this setup:

# Force all outgoing mail to use valid domain
sender_canonical_maps = regexp:/etc/postfix/sender_canonical

# Content of /etc/postfix/sender_canonical:
/^root@.*$/    noreply@yourdomain.com
/^.*@domain.local$/    noreply@yourdomain.com

Ensure your domain has proper DNS records:

• MX record pointing to your mail server
• Reverse PTR record matching your hostname
• SPF record authorizing your server

After making changes, verify and apply them:

postmap /etc/postfix/sender_canonical
postfix check
systemctl restart postfix

To test your configuration:

echo "Test email" | mail -s "Postfix Test" recipient@example.com
tail -f /var/log/mail.log

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When configuring a standalone Linux mail server using Postfix, you might encounter bounce messages stating "domain of sender address does not exist." This typically occurs when emails are sent from addresses like root@domain.local where the domain isn't properly registered or configured in DNS.

The primary files you'll need to modify are:

/etc/postfix/main.cf
/etc/postfix/generic
/etc/hostname
/etc/mailname

First, ensure your system's hostname and mail domain are correctly set:

# Set the hostname (replace with your actual domain)
sudo hostnamectl set-hostname mail.yourdomain.com

# Set the mail name
echo "yourdomain.com" | sudo tee /etc/mailname

Edit /etc/postfix/main.cf with these critical settings:

myhostname = mail.yourdomain.com
mydomain = yourdomain.com
myorigin = $mydomain
inet_interfaces = all
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
relayhost =
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
smtp_generic_maps = hash:/etc/postfix/generic

Create/edit /etc/postfix/generic to map local addresses to proper domain addresses:

root@localhost root@yourdomain.com
root@mail.yourdomain.com root@yourdomain.com
@localhost @yourdomain.com

Then compile the map:

sudo postmap /etc/postfix/generic

For proper email delivery, your domain must have these DNS records:

yourdomain.com.    IN  MX  10 mail.yourdomain.com.
mail.yourdomain.com. IN A   192.0.2.1 (your server IP)

Additionally, consider setting up:

• SPF record
• DKIM record
• DMARC record

After making changes, always reload Postfix:

sudo systemctl reload postfix

Test email sending:

echo "Test email body" | mail -s "Test Subject" recipient@externaldomain.com

If problems persist, check:

# View mail queue
postqueue -p

# Check logs
tail -f /var/log/mail.log

For better deliverability:

# In main.cf
smtpd_tls_security_level = may
smtp_tls_security_level = may
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key