MS Exchange server delivery error

Hi.
Yesderday i was sending mail, and all of the sudden, i got this message back from the administrator mailbox    " The message reached the recipient's e-mail system, but delivery was refused.  Attempt to resend the message.  If it still fails, contact your system administrator. #5.3.0".  The mail server was working fine for the whole day. I got the error by the end of the day. I didn't installed anything an no one worked on the server. The server is very slow and there's a lot of system errors. I did reboot the server and still got the erros.
Please help.
JacquesIIAsked:
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ahmedbahgatCommented:
possibly the destination server is rejecting yout mail because your server is listed on the internet as an open relay, this means your server has been spammed ie zillions of unsolicited mail are being relayed through your server

this may be the reason behind the errors you see and the slow down,

check the following:

the IMS queue
the IMS relay settings

you may also check the server for viruses

cheers
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BembiCEOCommented:
#5.3.0 is a non specific error, but it points to, what  ahmedbahgat said.

If your server is very slow, it may be that your server can not deliver the mail as it is heavily overloaded. The reason for this is often spam and as most of the mails can not be delivered, your server attempt to make periodicly connections to non existing servers, or your server delivers all the mails and have a lot of connections open. The system errors (which ones) may be the result of the overload.

Have a look at your SMTP queue, if you find a lot of emails in there, which are not targeting to your server, you are been hit by one or more spamers.

What is to do depends from your exchange version. Nevertheless, you have the close your server for open relay and check the blacklist, where you will then be listed and delete yoru entries.

To check yopur server for open relay, yust open a DOS BOX and type
telnet relay-test.mail-abuse.org

You can see, that this server will try to send mails to your server. All attempts must be responded by an RST or RSET (= connection reset).
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