main.py

import os
from datetime import datetime

key = "Subject: New scikit-learn questions"
path = '/Users/[  username  ]/Library/Mail/[  mailboxname  ]/INBOX.imapmbox/Messages/'
fnames = [p for p in os.listdir(path) if p.endswith('.emlx')]

times = []

for i,fname in enumerate(fnames):
    print i+1, "/", len(fnames)
    with open(path+fname) as f: txt = f.read()
    if key not in txt: continue
    date = [line for line in txt.split('\n') if line.startswith('Date:')][0][6:-6]
    date = datetime.strptime(date, "%a, %d %b %Y %H:%M:%S")
    times.append(date)

times = sorted(times)
deltas = [(times[i+1]-times[i]).total_seconds() for i in range(len(times)-1)]

seconds_in_24h = 86400.
times2 = [(t.hour*3600 + t.minute*60 + t.second)/seconds_in_24h*24 for t in times]

import matplotlib.pyplot as plt
plt.plot(times2)
plt.ylabel('Hour of day recieved')
plt.xlabel('Newsletters sorted by date')
plt.savefig('./newsletters-times.png', bbox_inches='tight')