When sending from Roundcube on an Ubuntu server with plesk, we get the following error:
SMTP Error (535): Authentication failed
Symptoms
While trying to send an email via Roundcube, the following error appears:
SMTP Error (535): Authentication failed
In /var/log/maillog following entries can be found:
warning: SASL authentication failure: cannot connect to saslauthd server: No such file or directory warning: SASL authentication failure: Password verification failed warning: localhost[::1]: SASL PLAIN authentication failed: generic failure
saslauthd service is running:
service saslauthd status
Redirecting to /bin/systemctl status saslauthd.service
● saslauthd.service - SASL authentication daemon.
Loaded: loaded (/usr/lib/systemd/system/saslauthd.service; enabled; vendor preset: disabled)
Active: active (running)
compatibility_level value was previously defined in /etc/postfix/main.cf as following:
# grep compatibility_level /etc/postfix/main.cf compatibility_level = 2
Here is the fix: Comment out compatibility_level in /etc/postfix/main.cf
Resolution
Login to the server via SSH.
Create a backup of /etc/postfix/main.cf:
# cp -p /etc/postfix/main.cf /etc/postfix/main.cf_bck
Remove compatibility_level value from /etc/postfix/main.cf using the favorite text editor.
# nano /etc/postfix/main.cf #compatibility_level = 2
Check SMTP daemon configuration:
If RHEL/CentOS/CloudLinux is used, verify that chrooted mode is disabled:
egrep "^smtp " /etc/postfix/master.cf | grep inet smtp inet n - n - - smtpd
If Debian/Ubuntu is used, verify that chrooted mode is enabled:
egrep "^smtp " /etc/postfix/master.cf | grep inet smtp inet n - y - - smtpd
Reload postfix configuration:
service postfix reload
Source: https://support.plesk.com/hc/en-us/articles/360004930633-Unable-to-send-an-email-from-Plesk-server-SMTP-Error-535-Authentication-failed