If you keep receiving emails that you would like to send back to your inbox, then there is a great chance that your IP is really blacklisted. That means, that you are not able to send any emails, until your IP gets deleted from the list. There are different ways how to get your IP from that list, but first, lets check that your IP is really blacklisted. The emails that you receive back should look something like this:

This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address (es) failed:
yourname@yourdomain.com
SMTP error from remote mailer after RCPT TO:
yourdomain.com [205.235.xxx.xxx]: 550-Message rejected because yourdomain.com [205.235.xxx.xxx] is blacklisted at
550 bl.spamcop.net see Blocked - see http://www.spamcop.net/bl.shtml? 205.235.xxx.xxx

The easiest way to get your email working again is just wait. Most of the IP’s get off the black list in 24 hours. If this does not help or you just do not want to wait so long, you should write an email to your host, and they should be able to help you with your problem and they can also tell you what exactly has been going on with your email address that it got blacklisted. Its probably a malicious software on your computer or a warez script on your web server that is sending out spam emails.

If you want to see who blocked your mail server IP address, check: http://www.moensted.dk/spam/. Enter the IP address and press Submit. 

If you would like to fix this problem as soon as possible, go to http://www.abuse.net/relay.html and enter your IP and email address and click on “Test for relay”. This can speed up the unlisting process, but the process can still last for 24 hours.

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