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Your outgoing mail server has been blacklisted...

17 June 2011

As an essential part of email security we subscribe to various public DNSBL (DNS-based Blackhole List, Block List, or Blacklist). These are used to publish the addresses of computers or networks linked to spamming.

All emails that arrive at our mail server are checked against various popular DNSBL, including SORBS, Spamhaus and SpamCop. If your outgoing mail server has been listed with one of those services, then the email is rejected/bounced with an error message:

Your outgoing mail server 61.9.189.231 has been blacklisted by SORBS - see Database Check - www.sorbs.net/

This allows us to block hundreds of spam and virus-laden emails a day from locations around the globe. Occasionally, however, a major ISP or webmail service such as Google, Bigpond or Hotmail are listed and this can cause problems for some of our clients.

Emails sent from/through a blacklisted server will not reach us, or clients for whom we manage emails. They will also be blocked from a number of major ISPs who subscribe to the same lists. The good news is that these blocks are only temporary.

In the meantime you can send emails using an alternative account such as Gmail, Hotmail or another ISP/network, or find out if the person you are contacting has an alternative email address or a contact form on their website that will also work.

We have no choice other than to filter emails in this fashion as failing to do so leads to our server being blacklisted, which is much bigger problem for more people.

This has become an issue in the last week mainly because BigPond has managed to have a number of their mail servers blacklisted on SORBS:

  • nskntmtas02p.mx.bigpond.com
  • nskntmtas03p.mx.bigpond.com
  • nskntmtas05p.mx.bigpond.com
  • nschwmtas02p.mx.bigpond.com
  • nschwmtas03p.mx.bigpond.com
  • nschwqsrv01p.mx.bigpond.com
  • nschwqsrv02p.mx.bigpond.com
  • nschwqsrv03p.mx.bigpond.com

Also a small number of Google servers:

  • smtp-out.google.com
  • mail-wy0-f171.google.com
  • mail-pv0-f186.google.com
  • mail-pv0-f186.google.com

In the last 36 hours we have blocked/rejected emails from over 400 mail servers, leading to around 900 emails being blocked.

Update: we have modified the configuration now to provide a gateway for emails from BigPond, Gmail and a number of other major networks to prevent them being blocked.

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