Excel function automatically resolve cell with 3/4 Letter code

hi folks,

in the picture you see the column "company" with 3/4 letter codes and the column
smtp with a smtp address in a worksheet called "ED"

in another worksheet called company_codes (see attached pic) i've for every 3 letter company code the domain like company "xxx = xxxexample.com"

Now i like to resolve the column "company" from the first picture in worksheet "ED"
with the long domain name in worksheet "company_codes" and write the result
to the end of the cells under column "SMTP" in worksheet "ED" at the end of the
smtp address behind the "@"

That means remove the short form xxx.com in "ED" SMTP and replace with
"xxxexample.com"

pls not be confused about the picture behind in the column "domain" you should see
the longform xxxexample.com instead of xxx.com

appreciate for your help