Reading mail from mbox folder using python

Question

I want to read mails from a mbox file and do some action based on that. I don't want to write/modify the mbox file but it will be modified by another process (Mostly adding new mails).

I am reading this documentation. http://docs.python.org/library/mailbox.html#mailbox.mbox

But I don't understand the following

1. Should I call lock() before reading the mail? (I am not writing to the file)
2. Is there anyway I can get a callback when other process (thunderbird) modifies the file?
3. Is the changes in the file reflected in the mbox object? I mean, after I create the mbox object, if a new mail is added to the file, will I access the message using the object? Or should I create a new object again?

PS: I am not allowed to install any plugins of thunderbird:(