Y.Turner@Hotmail.Com:Yvette Turner
Kelliekelly@Hotmail.Com:Kellie Kelly
Hades2056@Hotmail.Com:James Gillam
Peter.Garrad@Tesco.Net:Carl Garrad

Hades2056@Hotmail.Com
Peter.Garrad@Tesco.Net

file_1 = open('1.txt', 'r').read().split('n')
file_2 = open('2.txt', 'r').read().split('n')

array = []
for email in file_1:
    if email.split(':')[0] not in file_2:
        array.append(email)

str = ""
for email in array:
    str += email
    str += 'n'

file_3 = open('3.txt', 'w')
file_3.write(str)

import csv

fn1 = r'C:Temp.data616780_1.txt'
fn2 = r'C:Temp.data616780_2.txt'

with open(fn1) as f1, open(fn1 + '.new', 'w') as fout, open(fn2) as f2:
    mails = set(f2.read().splitlines())
    csv_writer = csv.writer(fout, delimiter=':', quoting=csv.QUOTE_MINIMAL)
    for row in csv.reader(f1, delimiter=':'):
        if not row[0] in mails:
            csv_writer.writerow(row)

Y.Turner@Hotmail.Com:Yvette Turner
Kelliekelly@Hotmail.Com:Kellie Kelly