US-only (hopefully) email regex (Trying to filter domains with out ''.jp or .co.uk")

Question

I'm using the current regex to match email addresses in Python:

EMAIL_REGEX = re.compile(r"[^@]+@[^@]+\.[^@]+")

This works great, except for when I run it, I'm getting domains such as '.co.uk', etc. For my project, I am simply trying to get a count of international looking TLD's. I understand that this doesn't necessarily guarantee that my users are only US based, but it does give me a count of my users without internationally based TLD's (or what we would consider internationally based TLD's - .co.uk, .jp, etc).

Answer 1

What you want is very difficult.

If I make a mail server called this.is.my.email.my-domain.com, and an account called martin, my perfectly valid US email would be martin@this.is.my.email.my-domain.com. Emails with more than 1 domain part are not uncommon (.gov is a common example).

Disallowing emails from the .uk TLD is also problematic, since many US-based people might have a .uk address, for example they think it sounds nice, work for a UK based company, have a UK spouse, used to live in the UK and never changed emails, etc.

If you only want US-based registrations, your options are:

• Ask your users if they are US-based, and tell them your service is only for US-based users if they answer with a non-US country.

• Ask for a US address or phone number. Although this can be faked, it's not easy to get a matching address & ZIP code, for example.

• Use GeoIP, and allow only US email addresses. This is not fool-proof, since people can use your service on holidays and such.

In the question's comments, you said:

Does it not make sense that if some one has a .jp TLD, or .co.uk, it stands to reason (with considerable accuracy) that they are internationally based?

Usually, yes. But far from always. My girlfriend has 4 .uk email addresses, and she doesn't live in the UK anymore :-) This is where you have to make a business choice, you can either:

1. Turn away potential customers
2. Take more effort in allowing customers with slightly "strange" email addresses

Your business, your choice ;-)

So, with that preamble, if you must do this, this is how you could do it:

import re

EMAIL_REGEX = re.compile(r'''
    ^             # Anchor to the start of the string
    [^@]+         # Username
    @             # Literal @
    ([^@.]+){1}   # One domain part
    \.            # Literal 1
    ([^@.]+){1}   # One domain part (the TLD)
    $             # Anchor to the end of the string
''', re.VERBOSE)

print(EMAIL_REGEX.search('test@example.com'))
print(EMAIL_REGEX.search('test@example.co.uk'))

Of course, this still allows you to register with a .nl address, for example. If you want to allow only a certain set of TLD's, then use:

allow_tlds = ['com', 'net'] # ... Probably more
result = EMAIL_REGEX.search('test@example.com')
if result is None or result.groups()[1] in allowed_tlds:
    print('Not allowed')

However, if you're going to create a whilelist, then you don't need the regexp anymore, since not using it will allow US people with multi-domain addresses to sign up (such as @nlm.nih.gov).