My guess is that you have the privileges set on your local box that
allow connections with those credentials but the same privileges are
not set up on your clients machines.
Although using apache as a user without a password is quite a security
risk. And then mailing those details to a public mailing list is
probably madness. I would suggest using a different username and
setting a password and then using those details to connect to the
database. Then set the same privileges on your client's machine