Question

I have a large number of email addresses to validate. Initially I parse them with a regexp to throw out the completely crazy ones. I’m left with the ones that look sensible but still might contain errors.

I want to find which addresses have valid domains, so given [e-mail] I want to know if it’s even possible to send emails to abcxyz.com .

I want to test that to see if it corresponds to a valid A or MX record – is there an easy way to do it using only Python standard library? I’d rather not add an additional dependency to my project just to support this feature.

Answer 1

There is no DNS interface in the standard library so you will either have to roll your own or use a third party library.

This is not a fast-changing concept though, so the external libraries are stable and well tested.

The one I’ve used successful for the same task as your question is PyDNS.

A very rough sketch of my code is something like this:

import DNS, smtplib  DNS.DiscoverNameServers() mx_hosts = DNS.mxlookup(hostname)  # Just doing the mxlookup might be enough for you, # but do something like this to test for SMTP server for mx in mx_hosts:     smtp = smtplib.SMTP()     #.. if this doesn't raise an exception it is a valid MX host...     try:         smtp.connect(mx[1])     except smtplib.SMTPConnectError:         continue # try the next MX server in list 

Another library that might be better/faster than PyDNS is dnsmodule although it looks like it hasn’t had any activity since 2002, compared to PyDNS last update in August 2008.

Edit: I would also like to point out that email addresses can’t be easily parsed with a regexp. You are better off using the parseaddr() function in the standard library email.utils module (see my answer to this question for example).