Hello

User "A" is using Outlook. He is sending mail to "B". Both have their
accounts at the same mailserver. "A" after sending is seeing this mail
in his sentbox. But "B" don't receive mail. Below is fragment server's
log:

192.168.2.1 [00000AB8] Tue, 13 Mar 2007 13:10:23 +0100 Connected
192.168.2.1 [00000AB8] Tue, 13 Mar 2007 13:10:23 +0100 220
mydomain.com ESMTP VisNetic.MailServer.v8.3.5.0; Tue, 13 Mar 2007
13:10:23 +0100
192.168.2.1 [00000AB8] Tue, 13 Mar 2007 13:10:23 +0100 HELO
wp09
192.168.2.1 [00000AB8] Tue, 13 Mar 2007 13:10:23 +0100 250
mydomain.com Hello wp09 [192.168.2.1], pleased to meet you.
192.168.2.1 [00000AB8] Tue, 13 Mar 2007 13:10:23 +0100 MAIL
FROM:
192.168.2.1 [00000AB8] Tue, 13 Mar 2007 13:10:23 +0100 250
2.1.0 ... Sender ok
192.168.2.1 [00000AB8] Tue, 13 Mar 2007 13:10:23 +0100 RCPT
TO:
192.168.2.1 [00000AB8] Tue, 13 Mar 2007 13:10:23 +0100 250
2.1.5 ... Recipient ok
192.168.2.1 [00000AB8] Tue, 13 Mar 2007 13:10:24 +0100 RSET
192.168.2.1 [00000AB8] Tue, 13 Mar 2007 13:10:24 +0100 250
2.0.0 Reset state
SYSTEM [00000AB8] Tue, 13 Mar 2007 13:10:43 +0100
Disconnected

As you can see sender and recipient are properly recognized by server.
After this Outlook is sending RSET and then server is waiting for
client. Client don't respond by 19 seconds so server is breaking
connection. Outlook even didn't try to send mail to server. But why
mail is in his sentbox?

Artur