CiviCRM Community Forums (archive)

While I agree that generally speaking, dedupes don't work the way you describe, in your case they shouldn't need to.  External identifier is defined at the database level as unique - you can't possibly have two external identifiers that are the same.  In which case you should only need to match on e-mail. Or am I missing something?

Ah!  I understand now.

It's actually quite common in my use of dedupes for there to be duplicates with different external identifiers.  Sometimes there are multiple external systems, and a contact might be in both.  Sometimes there's a legacy system with poor duplicate detection.

Now that I understand your use case though - I see where this can be a useful feature for some.  To be honest though, I don't think this will be prioritized by the core team, since I don't think many people will use it.  Most organizations don't have 100 contacts with the same e-mail, and if they do, they're likely to not use e-mail as their dedupe criterium.  So this would most likely have to come from a client who's invested enough to develop or fund it.

That said - the "civicrm_dedupe_exception" table is very simple, and I wouldn't hesitate to manualy update that via SQL.  So if your data has a lot of records that need to be dedupe exceptions, you can probably handle them with a single line of SQL.  You can do a "Cartesian Join" of the e-mail table to itself.  Something like:
INSERT INTO civicrm_dedupe_exception contact_id1, contact_id2 SELECT t1.contact_id, t2.contact_id FROM civicrm_email t1 JOIN civicrm_email t2 ON t1.email = t2.email WHERE t1.email = 'notdupe@email.org';