You're using a couple of terms which don't appear in Thunderbird, so we need to guess at what you mean. And this is quite understandable if you're not using an English language version of Thunderbird. https://support.mozilla.org/en-US/kb/how-create-and-use-mailing-lists-thunderbird If your "group" is in fact a Mailing List, then yes, you should expect any Contact in the Mailing List to also appear in the associated address book. A Mailing List is a subset of its host address book. So, it's correct for the added Contact to appear in the PAB. Your problem may be that the Mailing List is broken and won't accept new Contacts being added to it. The usual solution is to make a new Mailing List. You should be able to drag and drop the contents of the old list into the new. When the new Mailing List is proven to work, delete the old one to avoid confusion about which is which. Alternatively, this might come about from the way you add your new Contact. If your "group" is an address book and not a Mailing List, and you are adding the new Contact by clicking its white star, then by default that Contact will be added to PAB. After adding, you need to click its star again, which will now be yellow, select Edit and choose which address book you want it stored in.