LinuxPizza

First, list the users that you have in your system:

sasldblistusers2
selea@mailserver.linux.pizza: userPassword
pizza@localhost: userPassword

Next, change the password of the specific user you want to change:

saslpasswd2 pizza@localhost                                            
Password:
Again (for verification):

That's it!

If you want to create a new user

saslpasswd2 -c -u domain.tld smtprelay

You can also test a SASL-user with the following:

testsaslauthd -u smtprelay -r domain.tld -p PASSWORD