import pandas as pd
import os
import re


#fetching the mail adress through indexnumber out of the list
with open('Protected/Protected G.txt', 'r') as file:

    #creating the regex pattern to sort out the mail adresses
    rgx = 'S+@S+'

    #read the file and convert the list into a string
    content = file.readlines()
    content_str = ''.join(content)

    #get the mails out of the "list" with regex
    mails = re.findall(rgx, content_str)

    #put each mailadress in a variable
    for item in mails:
        print(item)

Dummy-Dataframe:

    Forename    Last Name   Email           Protection

1   John        Kennedy     John@gmx.net

2   Donald      Trump       Donald@gmx.net

3   Bill        Clinton     Bill@gmx.net

4   Richard     Nixton      Richard@gmx.net

Finished Dataframe:

    Forename    Last Name   Email           Protection

1   John        Kennedy     John@gmx.net    x

2   Donald      Trump       Donald@gmx.net  o

3   Bill        Clinton     Bill@gmx.net    x

4   Richard     Nixton      Richard@gmx.net x