Knowledgebase
Why are my emails bouncing back?
Posted by Sean Syed on 20 February 2013 06:35 PM

Spam filters will often check against Realtime BlockLists (RBLs) to check if the sending IP address is from a legitimate source. If an IP address has been blocklisted the decision whether to accept your email for delivery is not based on the content of the email or the email address that it comes from or is addressed to. It is based solely on the mail server that is being used by the sender. An IP address may be listed for a number of reasons, however the most common are that you are sending email from:

  • a mail server that has been listed

  • a dynamic IP address

  • an open proxy, relay or exploited machine.

 

What to do if an IP address has been blocklisted

 

If the IP address that you are using to send emails has been blocklisted you will recieve a returned email from ourselves.

A typical returned email will look like this.

Nov 28 11:01:07 smtpin-2-12 postfix/smtpd[2975]: NOQUEUE: reject: 

CONNECT from 72-255-38-44.client.stsn.net[72.255.38.44]: 554 DNN4Less is not accepting mail from [ Client host ; 72.255.38.44 ] at this time.
Please contact abuse@
DNN4Less.co.uk quoting this full error message.
cbl.abuseat.org; Blocked - see
http://cbl.abuseat.org/lookup.cgi?ip=72.255.38.44; Reason for listing proto=SMTP

The sections highlighted in this returned message show the IP address sending the email, the company who have listed the IP address, and the reason why the IP address has been listed.

Error messages may differ slightly in layout, however the information contained within them will remain the same.

 

If the message shows Blocked via DNN4Less RBL then the IP address sending the mail has been blocked by DNN4Less' blocklist.

 

Using a dynamic IP address

This is an example bounceback where the sender has attempted to send email from a dynamic IP address.

Diagnostic-Code: SMTP; 554 DNN4Less is not accepting mail from [ Client host ; 112.250.116.241 ] at this time. (dnsbl.sorbs.net; Dynamic IP Addresses See: http://www.sorbs.net/lookup.shtml?112.250.116.241).  Contact abuse@DNN4Less.com if you believe this to be in error.

Due to the increase in trojans and virus's sending spam from infected machines, almost all emails originating from dynamic IP addresses are spam. To protect our customers interests we are not able to accept email directly from a dynamic IP address. If you are using a dynamic IP address please ensure that you are sending email via a designated SMTP server. This server will either by provided by your ISP or by the provider of your email service. If you are using DNN4Less as your Internet service provider, or are sending email from an advanced mailbox you can use DNN4Less SMTP servers to send email.

Using a static IP address

The following example bounceback has been returned as a complaint regarding unsolicited email has been reported as originating from this IP address.

554 DNN4Less is not accepting mail from [ Client host ; 192.168.111.52 ] at this time.  Please contact abuse@DNN4Less.com quoting this full error message.
dnsbl.sorbs.net; Spam Received withing last 12 months See:
http://www.sorbs.net/lookup.shtml? 192.168.111.52 Spam Received Recently See: 
http://www.sorbs.net/lookup.shtml? 192.168.111.52

If you are the administrator of the listed IP address

This email has been returned as a complaint has been made regarding unsolicited, or abusive email originating from this server. Additionally this server may be listed as an open proxy, relay or may be an exploited machine. As the administrator of the IP address listed in this message you should ensure that no unsolicited email is sent from this IP address then contact the company that has you listed. This can be found in the link provided within the returned email. You can then request that they remove your IP address from their records.

If you are sending email through a designated mailserver

Any internet service provider who does not actively take precautions to limit the likelihood of unsolicited email being sent through their servers runs the risk of having the IP addresses involved blocklisted. If your internet service providers mail server has been identified by a blocklist as a source of unwanted or abusive email you should contact them directly. They may require the header of a bounced email to investigate fully.

 

DNN4Less can only act to help fix this problem if you are sending email through a DNN4Less mail server and it is our mail server that has been blocked. If the email that is not being delivered was not sent from a DNN4Less account and through a DNN4Less mail server then we will not be able to act to resolve this issue.

 

All scripts placed in a directory called bin in htdocs will fail to execute. You should either move the files to another folder and remove the folder, or rename the folder.

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