After someone registers I always receive 2 replies like this >>>TO: registration@xxxxxxxxxx.net; admin@xxxxxxxxx.net<<<<<, where can I fix this?
use only one admin account. Registration confirmation is being sent to all admin accounts. You could edit the code and manually make it send the email only to one admin account.
If you only have one admin account, make sure that it doesn't differ from the email address in coppermine's config.