[Mailman-Developers] Suggestions about Mailman bounce processing

[Mark Sapiro]

Superticker2 (Mark) wrote:
>
>If there's a service or utility that can verify a list of email addresses
>(prior to a mass operation), please suggest it.


There are some. See for example
<http://www.tienhuis.nl/php-email-address-validation-with-verify-probe>
or try this google search
<http://www.google.com/#q=verify+email+address>.

There are problems with trying to do address verification without
actually sending mail. The obvious way to verify an address is to send
an SMTP VRFY command to the MX of the domain of the address, but these
days most SMTP servers either don't implement VRFY or won't accept
VRFY from untrusted sources.

The alternative is to begin an SMTP dialog with the MX and send MAIL
FROM and RCPT TO commands. As long as you don't send DATA, no mail
will actually be sent, but this is not reliable. If the MX rejects the
RCPT, you may know from the status that the address is bad, but some
MXs will accept an invalid RCPT address and not respond with failure
until after DATA, and you can't continue to that point if you don't
want to actually send mail.


For example, consider the following two SMTP sessions

$ telnet a.mx.mail.yahoo.com 25
Trying 67.195.168.31...
Connected to a.mx.mail.yahoo.com (67.195.168.31).
Escape character is '^]'.
220 mta178.mail.ac4.yahoo.com ESMTP YSmtp service ready
HELO msapiro.net
250 mta178.mail.ac4.yahoo.com
MAIL FROM: <mark at msapiro.net>
250 sender <mark at msapiro.net> ok
RCPT TO: <totally_bogus_mark_sapiro at yahoo.com>
250 recipient <totally_bogus_mark_sapiro at yahoo.com> ok
DATA
354 go ahead
.
554 Transaction failed: empty DATA not allowed
Connection closed by foreign host.

and

$ telnet a.mx.mail.yahoo.com 25
Trying 67.195.168.31...
Connected to a.mx.mail.yahoo.com (67.195.168.31).
Escape character is '^]'.
220 mta112.mail.ac4.yahoo.com ESMTP YSmtp service ready
HELO msapiro.net
250 mta112.mail.ac4.yahoo.com
MAIL FROM: <mark at msapiro.net>
250 sender <mark at msapiro.net> ok
RCPT TO: <totally_bogus_mark_sapiro at yahoo.com>
250 recipient <totally_bogus_mark_sapiro at yahoo.com> ok
DATA
354 go ahead
From: me
To: you

body
.
554 delivery error: dd This user doesn't have a yahoo.com account
(totally_bogus_mark_sapiro at yahoo.com) [0] - mta112.mail.ac4.yahoo.com
Connection closed by foreign host.

-- 
Mark Sapiro <mark at msapiro.net>        The highway is for gamblers,
San Francisco Bay Area, California    better use your sense - B. Dylan