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The issue was with your dedupe rules as you had not entered weights. You can't leave the weights empty. 

Try reading civicrm.org/blog/spidersilk/understanding-civicrm-dedupe-rul‌​es or https://docs.civicrm.org/user/en/stable/common-workflows/deduping-and-merging/. 

I think the former makes it a bit clearer about weight. But basically you need to have a weight, eg email 2 first 10 last 10; threshold 22, so that it means it must score a match on the email AND the first AND the last

reason for a lower 'score' on the email is that if a contact has 4 emails all of which are the same, then each 'counts' hence if you set email as 10, and first as 10 and last as 10, threshold 30, then the email by itself would score a 40 and hence 'match' even if first and last did not match! hope that helps