I have a mail server on windows 2003 ( MailEnable) I setup mail server to authonticate users before sending mail. (This mail server requires authentication when attempting to send to a non-local e-mail address) but from yesterday , without change any setting I got many Message Delivery Delay from mail server for email address that I never try to sending email: I afraid that I someone try to sending Spam from my mail server,How can I check this possiblity ? and fix the problem.
MailEnable: Message delivery has been delayed.
Message is waiting at *****.info for delivery to mailin-03.mx.aol.com.
The message will be retried for another 29 hours.
Reason: Mail Server for aol.com could not accept your email at this time. MailEnable will keep trying to deliver this message and will notify you of any progress.
The remote mail server returned the error: 421-: (DNS:NR)