When configuring Postfix with SMTP authentication using SASL, you might encounter the frustrating "cannot connect to saslauthd server" error. The key symptoms include:

• Failed authentication attempts with "535 5.7.8 Error: authentication failed"
• Log entries showing "SASL authentication failure: cannot connect to saslauthd server"
• Successful tests with testsaslauthd but failures in actual Postfix operation

First, let's check the existing setup based on the information provided:

# Current smtpd.conf configuration
pwcheck_method: saslauthd
mech_list: PLAIN LOGIN
saslauthd_path: /var/run/saslauthd/mux
autotransition:true

# Postfix main.cf entry
smtpd_sasl_auth_enable = yes

1. Check saslauthd Process Status

ps aux | grep saslauthd
systemctl status saslauthd

If saslauthd isn't running, start it with the correct parameters:

saslauthd -a shadow -m /var/run/saslauthd -n 5

2. Verify Socket Path Accessibility

The most common root cause is Postfix (running in chroot) being unable to access the saslauthd socket. Check these paths:

ls -la /var/run/saslauthd/
ls -la /var/spool/postfix/var/run/saslauthd/

Create the necessary directory structure if missing:

mkdir -p /var/spool/postfix/var/run/saslauthd
chown postfix:sasl /var/spool/postfix/var/run/saslauthd
mount --bind /var/run/saslauthd /var/spool/postfix/var/run/saslauthd

3. Update Postfix Configuration

Modify your /etc/postfix/sasl/smtpd.conf:

pwcheck_method: saslauthd
mech_list: PLAIN LOGIN
saslauthd_path: /var/spool/postfix/var/run/saslauthd/mux
log_level: 3

Enable verbose logging in saslauthd:

saslauthd -d -a shadow -m /var/run/saslauthd

Check authentication attempts in real-time:

tail -f /var/log/auth.log

1. Ensure saslauthd is running with correct parameters
2. Verify socket path exists in Postfix chroot environment
3. Confirm proper permissions on all directories
4. Check that SELinux/AppArmor isn't blocking access
5. Restart both saslauthd and Postfix after changes

After applying these changes, test authentication again:

telnet localhost 25
EHLO example.com
AUTH PLAIN AHRlc3R1c2VyAHRlc3RwYXNzd29yZA==

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When setting up SMTP authentication in Postfix, you might encounter the frustrating SASL error where Postfix can't locate the saslauthd socket. The critical error message appears as:

warning: SASL authentication failure: cannot connect to saslauthd server: No such file or directory

Interestingly, testsaslauthd works fine but Postfix fails to authenticate users, indicating a path or permission issue rather than a complete SASL setup failure.

First verify these essential components:

# Check saslauthd status
systemctl status saslauthd

# Verify socket path
ls -la /var/run/saslauthd/mux

# Test SASL directly
testsaslauthd -u username -p password

Many Postfix installations run in a chroot jail. If your master.cf shows entries like this:

smtp      inet  n       -       y       -       -       smtpd

The 'y' indicates chroot is active. You'll need to mirror the saslauthd socket path inside the chroot:

mkdir -p /var/spool/postfix/var/run/saslauthd
mount --bind /var/run/saslauthd /var/spool/postfix/var/run/saslauthd

Edit /etc/default/saslauthd with these key settings:

START=yes
MECHANISMS="shadow"
OPTIONS="-c -m /var/run/saslauthd"

Then restart saslauthd:

systemctl restart saslauthd

Your /etc/postfix/sasl/smtpd.conf should contain:

pwcheck_method: saslauthd
mech_list: PLAIN LOGIN
saslauthd_path: /var/run/saslauthd/mux
log_level: 3

And in main.cf add:

smtpd_sasl_auth_enable = yes
smtpd_sasl_security_options = noanonymous
smtpd_sasl_local_domain = $myhostname
broken_sasl_auth_clients = yes

Enable verbose logging in saslauthd:

saslauthd -a shadow -d

Check the mail logs in real-time:

tail -f /var/log/mail.log

Verify SASL capabilities in Postfix:

telnet localhost 25
EHLO example.com

Look for AUTH capabilities in the response.

If you're still facing issues, consider:

# Change authentication method
pwcheck_method: auxprop
auxprop_plugin: sasldb

# Or use PAM directly
pwcheck_method: pam

Remember to create appropriate sasldb entries if changing methods:

saslpasswd2 -c -u example.com username