RE: strange SMTP behaviour

Hi,

Thanks for posting here.

Based on the information, I suggest that we perform the following steps
troubleshooting:

1. Let's use telnet utility to repro the SMTP session:

a) On the Exchange server 2003, type "telnet" (without the quotation marks)
and press ENTER at the command prompt.

b) At the Microsoft Telnet command prompt, type "set LOCAL_ECHO" (without
the quotation marks), and then press ENTER.

c) Type "open <server_name > 25" (without the quotation marks), and then
press ENTER.

Note: Use the same servers as you see in the log.

d) Begin communication by typing the following command:

HELO mail.mydomain.com

What responses do you see? If the connection is not dropped, continue with
the following commands.

e) Type the following command to tell the SMTP server whom the message is
from:

MAIL FROM:<username@xxxxxxxxxxxxxxxx>

NOTE: You should replace the sender's e-mail address with your e-mail
address.

f) Type the following command to tell the SMTP server whom the message is
to.

RCPT TO:<recipient@xxxxxxxxxxxxxxx>

NOTE: You should replace the recipient's e-mail address with the one you
fail to send.

g) Type the following command to tell the SMTP server that you are ready to
send data:

DATA

h) Type the message body.

This is just a test mail!

i) Type a period at the next blank line, and then press the ENTER key to
indicate the end of the message.

j) Close the connection by typing the following command:

QUIT

2. Can you send the testing mail successfully in telnet session?

3. Based on the information, it seems that the remote mail server performs
the reverse DNS lookup. The SMTP connection might be rejected if the
reverse DNS record is not created correctly for your Exchange server. There
are some third party websites that can help to check the reverse DNS
resolution. Let's try the following two websites to verify:

a) http://www.dnsstuff.com/

Choose the "Reverse DNS lookup" at the middle column. Fill in the IP
address of your Exchange server, and click RevDNS button to perform reverse
DNS lookup.

b) http://www.all-nettools.com/

Fill in the IP address of your Exchange server under NsLookup section, and
click GO! button to perform reverse DNS lookup.

======
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======

If the reverse DNS lookup failed, normally you need to fix the PTR record.

4. If the reverse DNS lookup complete properly make sure that the FQDN name
is the same as the one specified in HELO command. (HELO mail.mydomain.com)

If anything is unclear, please feel free to let me know. I'm looking
forward to your reply.

Have a nice day.

Best Regards,

Steven Zhu
MCSE/MCDBA
Microsoft Online Partner Support
Get Secure! - www.microsoft.com/security
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