class Email(models.Model):
    sent = models.BooleanField(default=False)
    subj = models.CharField(max_length=140)
    msg = models.TextField()

from django.db import connection
[...]
class EmailLocks(object):
    def __init__(self):
        self.c = connection.cursor()
    def __enter__(self):
        self.c.execute('''lock tables my_app_email write''')
    def __exit__(self, *err):
        self.c.execute('unlock tables')

with EmailLocks():
    # read the email table and decide if you need to process it
    for e in Email.objects.filter(sent=False):
        # send the email
        # mark the email as sent
        e.sent = True
        e.save()

* * * * * /usr/bin/flock -n /tmp/fcj.lockfile /usr/bin/python /home/txuser/dev/Project1/projectnew/manage.py flocktest