gContactSync version 3 will have a new, optional feature to ignore contacts without e-mail addresses to address the common complaint about contacts with “dummy” e-mail addresses (nobody…@nowhere.invalid). This will be configurable in each synchronized address book, and will be off by default in existing synchronized address books for forward compatibility.
Contacts that do not have any e-mail addresses will be ignored by the synchronization process. This means that if you remove all e-mail addresses from a contact that was previously synchronized gContactSync will consider it to have been “deleted” and will delete the contact from the other source.
Version 3.0.0a1 is on the development channel on addons.mozilla.org if anyone wants to try this new feature.