Creating a pythonic snippet to read and clean .csv files
Firstly, you should raise not return your errors.

Secondly, try: with a bare except: is bad practice (e.g. http://blog.codekills.net/2011/09/29/the-evils-of--except--/); what do you expect could go wrong with each step? Test for specific errors and deal with them appropriately. It is this which has hidden the NameError I mention at the end.

Thirdly, your use of the flag err seems a bit odd; much more Pythonic to use an actual boolean err = False or, better, else::

try:
    validate_email(e_mail) # see comment below
except: # but only the errors you expect - see above 
    pass
else:
    cleaned_csv_content.append((fname, lname, e_mail)) # note additional parentheses


or, even better, refactor validate_email to return True for a valid email and False otherwise, rather than raising errors:

if validate_email(e_mail):
    cleaned_csv_content.append((fname, lname, e_mail))


Finally, note that "email" != "e_mail".