User needs to type in the password to send an email
def send_mail() :


Per PEP8, you wouldn't typically include a space before those colons. You should run your code through a linter.

password = input("Password :")


This is a big no-no. Never expose a user's password content on the screen if you can avoid it. Instead, use the built-in getpass which attempts to mask your input.

mail.close()


You should avoid doing this explicitly, and instead use mail in a with statement.

'3 attempts before locking you out for 10 seconds.'


This line has no effect. Perhaps you meant to write print here. Also, don't hard-code the 3 in the string; use num_of_tries.