is the Account ID from Account table primary key?

In my account table, every time when I create a account, zoho automatically creates a account ID for that account. For my understanding, account ID should be the primary key. But it seems like it  is not because when I export some accounts with the same account name, update them and re-import in zoho according to their respective account ID,  all the info go to the 1st account name that has been created. So zoho does not take into consideration the account ID during the importation. I have the same problem with Contact table. It seems like Zoho considers email as primary key however, in my Contact table, a lot of contacts use the same email, so during the importation, all the info go to the first email created and the others are seen as duplicate. is there any solution for that?

thanks

Blanche