Re: Email users

[Jeff <jeff virgin net>]

On Fri, 2004-02-06 at 14:57, Rudolf A. A. wrote:
> Hello,
>  
> I have a question about sendmail and mail in general.
>  
> I want to know is it possible to know if there are some specific users
> in some specific servers.
> for example On mydomain.com I have user myuser mydomain com, and
> people from outside want to know if this user exists or not ?, so how
> can they do that ?. I mean to know this, without sending email.
> Otherwise they can send email, and if the mail does not come back, It
> means the user exists :).
> Or without sending email to him, how can I know, is there a such user
> ivantan singtel com  ?.
>  
> Thanks in advance.
> Rudolf.
>  

Although the method below may not work on some systems (Ed's example for
instance) it will work on most...

Telnet the receiving MTA, begin the start of the SMTP protocol and quit
before sending the mail. For example...


<response for a VALID mailbox>

telnet mta 25
Trying 192.168.0.1...
Connected to mta.
Escape character is '^]'.
220 ESMTP Sendmail 8.12.8/8.12.8; Fri, 6 Feb 2004 22:03:59 GMT
helo beast
250 Hello beast [192.168.0.2], pleased to meet you
mail from: <some user hotmail com>
250 2.1.0 <some user hotmail com>... Sender ok
rcpt to: <valid user yourdomain com>
250 2.1.5 <valid user yourdomain com>... Recipient ok
quit
221 2.0.0 closing connection
Connection closed by foreign host.

<response for a INVALID mailbox>

[saultj beast saultj]$ telnet mta 25
Trying 192.168.0.1...
Connected to mta.
Escape character is '^]'.
220 ESMTP Sendmail 8.12.8/8.12.8; Fri, 6 Feb 2004 22:07:02 GMT
helo beast
250 Hello beast [192.168.0.2], pleased to meet you
mail from: <some user hotmail com>
250 2.1.0 <some user hotmail com>... Sender ok
rcpt to: <invalid user yourdomain com>
550 5.1.1 <invalid user yourdomain com>... User unknown
quit
221 2.0.0 closing connection
Connection closed by foreign host.


Again, not 100% accurate but works on most setups.

HTH
Jeff