If you mean there's an email address shown under the user's profile, it could mean the following:
- The user allowed email to be shown, setting "Show email address to others?" option to "Yes";
- While working out your custom membership auth, you didn't put 'user_viewemail' in the table of users, which is a mandatory field for miniBB and which value should be set to '0' by default; i.e. all emails are hidden until allowed by the user. You could also remove this option from the public profile's template, setting it always to '0' in your custom table; but it should be there.