Alguém sabe onde ta dando o erro?

arquivo = open('mbox.txt', 'r')
arquivo.readline()

soma = 0
cont = dict()
lista = ()

for linha in arquivo:
    if linha.startswith('From'):
    arroba = linha.find('@')
    emails = linha.split()(1)
    lista = (emails)
    lista.extend(lista)
    print(lista)

    for palavra in lista:
        cont(palavra) = cont.get(palavra, 0) + 1

print(cont)

output:

….
mbreuker@loi.nl
mbreuker@loi.nl
ajpoland@iupui.edu
ajpoland@iupui.edu
rjlowe@iupui.edu
rjlowe@iupui.edu
rjlowe@iupui.edu
rjlowe@iupui.edu
a.fish@lancaster.ac.uk
a.fish@lancaster.ac.uk
a.fish@lancaster.ac.uk
a.fish@lancaster.ac.uk
a.fish@lancaster.ac.uk
a.fish@lancaster.ac.uk
dlhaines@umich.edu
dlhaines@umich.edu
mbreuker@loi.nl
mbreuker@loi.nl
david.horwitz@uct.ac.za
david.horwitz@uct.ac.za
zach.thomas@txstate.edu
zach.thomas@txstate.edu
jimeng@umich.edu
jimeng@umich.edu
zqian@umich.edu
zqian@umich.edu
jzaremba@unicon.net
jzaremba@unicon.net
colin.clark@utoronto.ca

Traceback (most recent call last):
File "C:UsersskylaPycharmProjectspythonProjectTestescontar_palavras.py", line 12, in
emails = linha.split()(1)
IndexError: list index out of range

repositório do txt https://github.com/StrongerFX69/TXT