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sendmail error 503 5.0.0 Need MAIL befor

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7 replies

by beckas

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Hi

I am not familiar with sendmail at all (I am a Microsoft Exchange
Administrator) so I really need some help from you experts. My
company is not able to send to another company that uses sendmail as
their e-mail platform. We receive the following bounce back message
when mailing to them:

Unexpected recipient failure - 503 5.0.0 Need MAIL before RCPT

The sendmail e-mail administrator swears that there is not a problem
with his server and that it's a problem on my side yet I sent them the
dialog that my e-mail server had with his and the dialog states that
the message was passed to his e-mail server.

Now I don't understand how sendmail resolves but I'm guessing that
these people don't have the 'accept_unresolvable_domains' enabled on
their sendmail server and their server is not resolving my domain. If
this is the case, how does sendmail resolve a domain? Does it only
use DNS recors? I ask because my domain is configured not to reply to
ping requests for security reasons. I am not aware of any DNS
misconfigurations with any ISPs in regards to my company.

Funny thing is that the sendmail administrator rebooted his sendmail
server the other day and things were temporarily fixed for a day. Now
the problem is back again.

Can anyone give me some advice on what I should do to troubleshoot
this? I'm really frustrated that the sendmail administrator is making
this my problem and does not have any knowledge on how to troubleshoot
this problem.

Thanks,

Rebekah

7 replies

by cpfeiffe

For resolution sendmail will use DNS by default. If a mail domain is not in DNS it will fail, but the error will be different. The sendmail server won't need to ping your server, it will just need to find your domain in DNS. In sendmail you can configure other resolution methods and add specific domains to accept mail from, but I don't think this is the problem you are having based on the error.

More than likely the problem is with your mail client. This typically occurs if you send mailfrom some mail clients with the option "smtp batch on". Switching to "smtp batch off" will hopefully fix this. This is a security precaution on the Sendmail server side. Your server is sending the rcpt before the actual message and Sendmail doesn't want to accept it that way because an unvalidated rcpt might be a buffer attack attempt. Here is a link to one short example that describes such a scenario.

http://www.febo.com/list-archive/nos-bbs/9410/msg00255.html

Good luck.

by beckas

Hi Charles

A couple of questions if you don't mind. First of all, all of the people in my company use Microsoft Outlook and I am not aware of any "smtp batch off" configuration setting on the client side. What exactly does this command do? Have you heard of such a setting existing on an e-mail server rather than on a client? I am not familiar with the terminology. Maybe Microsoft calls it something different.

Secondly, the link to your article did not work. Can you please post the article?

Thank You,

Rebekah

by superboy650

Here is a example of sendmail server receiving
mail.

>>> 220 mail.mailserver.com ESMTP Sendmail 8.11.6/8.8.7; Fri, 10
May 2002 16:17:59 -0700
<<< helo ccs
>>> 250 mail.mailserver.com Hello , pleased to meet you
<<< mail from: test@test.com
>>> 250 2.1.0 test@test.com... Sender ok
<<< rcpt to: mail@mailserver.com
>>> 250 2.1.5 mail@mailserver.com... Recipient ok
<<< data
>>> 354 Enter mail, end with "." on a line by itself
<<< from: test@test.com
<<< subject: testing
<<< email test
<<< .
>>> 250 2.0.0 g4ANIKj10428 Message accepted for delivery

Your mail client must send the
MAIL FROM: user@domain.com before sending the RCPT TO: mail@mailserver.com

If not sendmail returns the need MAIL before RCPT
error

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