import re

parts = ["@gmail", "@cngmail.", "google", "hotmail"]

test = "[email protected],  "
test2 = test.replace(" ","").replace(",","")
#cut-off comma and whitespaces at the end

print(test2)   # [email protected]
print(parts[0]) # @gmail

print(parts[0] in test2)
print(re.search(parts[0], test2))
print(test2.rfind(parts[0]))

[email protected]
@gmail

False
None
-1