How to update Table B from Table A if No duplicate email in Table B?

Transact-SQL
1

I have Table A and Table B . I need to update Table B email address matching with Table A CUSTOMER_ID. But before updating Table B I need to check if the same email address exists with another CUSTOMER_ID in the table Table B don't update that email address.

example tables

Table A           
CUSTOMER_ID   PRIMARY_FLAG    ACTIVE_FLAG FORMATTED_PHONE_ADDRESS
1033695           Y           Y           abcxyz@sproule.com
1076561           Y           Y           utam@gmail.com
1099936           Y           Y           peiman@gmail.com
1191873           Y           Y           abdulhakim@redmail.com
1297902           Y           Y           kbibault@hotmail.ca
1310143           Y           Y           chikwcj@chevron.com
1316231           Y           Y           marco.nieto@bestmail.com
1563840           Y           Y           aghafour@live.com
1650308           Y           Y           surajeetrath@yahoo.co.in
1701499           Y           Y           osamaelbakly@gmail.com

Table B  
CUSTOMER_ID PRIMARY_EMAIL_ADDRESS 
1033695     abcxyz12@hotmail.com 
1076561     NULL 
1099936     NULL 
1191873     peiman@gmail.com 
1297902     abdulhakim.nahdi@aramco.com 
1310143     chikwcj@gmail.com 
1316231     NULL 
1563840     NULL 
1650308     aghafour@live.com 
1701499     osamaelbakly@egas.com.eg

I want result like

Update only non-duplicate email address

Update CUSTOMER Table

CUSTOMER_ID     PRIMARY_EMAIL_ADDRESS
1033695         abcxyz@sproule.com
1076561         utam@gmail.com
1310143         chikwcj@chevron.com
1316231         marco.nieto@bestmail.com
1701499         osamaelbakly@gmail.com

I hope My question is understand

2

No.

Why are the following not in the results?

CUSTOMER_ID      FORMATTED_PHONE_ADDRESS
1191873          abdulhakim@redmail.com
1297902          kbibault@hotmail.ca
1650308		     surajeetrath@yahoo.co.in