Any user name should be ok (including "mailuser") as long as the pair user/password created to access the mysql database and the pair user/password you tell postfix and dovecot to use in the config files are the same.

Hello,

Check your password for mailuser again in the the file /etc/postfix/mysql-virtual-alias-maps.cf

I have the same problem.
User and password are correct. In fact, I can access mysql>

Here is the cf file:

cat mysql-virtual-mailbox-domains.cf

user = mailuser
password = mypassword
hosts = 127.0.0.1
dbname = mailserver
query = SELECT 1 FROM virtual_domains WHERE name='%s'

if I change user = root, and password = rootpassword

then it works.

But… that is not right, right?

The MySQL administrator (called "root" in your example) IS NOT the same as the super-user account called "root".

If you want to disambiguate them, create a new MySQL user (say "dbadmin") with a different password and give "dbadmin" all the same PRIVILEGEs as the MySQL account "root". Then log in to MySQL as "dbadmin" and delete the MySQL account "root".

With respect to your issue with "mailuser", did you give "mailuser" the correct PRIVILEGE to read the "virtual_domains" table? You should try your query manually using the mysql(1) command shell.

-- sw