I was told by a rep that auto Contact deduping is done via both email address match and phone number match. For most B2B businesses auto-deduping by phone number is a HUGE problem, as multiple staff members interacting with you may list their office number, but you certainly want to retain separate Contacts with unique emails for each of them.

Ultimately there needs to be an option to turn on/off which fields are used for auto dedupe - at the very least for the phone value.