recipient validation with smtplib

[Tim Williams]

On 28/09/2007, Robin Becker <robin at reportlab.com> wrote:
> Is there a way to use smtplib to get recipient validation. I can use smtplib
> quite happily to send emails using the locahost's sendmail, but sendmail is just
>  fire and forget, so some bad addresses eg idiot at www.dingo.zzz don't cause any
> error in the sending application. I know some smtp setups do enforce recipient
> validation, but it doesn't seem terribly easy to do this with sendmail. I
> wondered if there were some way to do this in python?

There is no way of  validating *every* email address you send to using
SMTP alone.   Some servers accept every address and bounce later - as
you have found out. So for the purpose of the SMTP client, or relaying
server,  the address is valid at sending time to those servers.

Checking DNS for MX records is a possibility for removing some bad
addresses, but it's not fool proof as the RFCs don't require MX
records to exist for a domain to be able to receive email.  If no MX
records are present, one (and only one!) IP address returned from the
domain's A record(s) should be tried.

HTH :)