Diagnosis

Your emails do not reach their intended recipient.  Instead, you receive a notification that your email was not delivered.  In the technical explanation, it states that the IP address is blacklisted.

Note: There are many other reasons for email not to be delivered.

Explanation

SORBS is one of several global organisations fighting spam.
They have a database of alleged spammers.
The identity of the alleged spammer is their IP address.
This is a unique number assigned to each computer on the Internet.

The IP addresses of alleged spammers are gathered using a variety of automated and manual methods.
The process is prone to error, and you may end up blacklisted with little justification.

Internet Service Providers subscribe to the blacklist service in order to reduce the amount of incoming spam to their customers.
Each email being sent to that ISP is checked to see if the sender IP is blacklisted.
This means that if your IP address is in their database, your email will be blocked.

The problem

There are several problems with this approach:

1. You have no control over the path that your email travels through the Internet.
   If your email passes through a server that is blacklisted in the SORBS database, your email will be blocked, even though you are not a spammer.
   Every time you send an email, it can potentially travel a different route through the Internet.
   This means that some of your emails may get through to the recipient, and others not. 
   
   
2. Your IP address is temporary and is re-used.
   Every time you reconnect your ADSL or dialup account, you are assigned a new IP address.
   If the IP address was recently used by a spammer, it will be blacklisted, and your email will be blocked. 
   
   
3. Your service provider may be blacklisted.
   Most service providers operate a group of IP addresses.
   If one of their subscribers has been blacklisted, it may affect all other users in that IP group.
   
   
4. You may use different IP addresses during the day.
   For example, if you send emails in the office, they go via ADSL to ISP number 1.
   When you are out of the office, you send via 3G using ISP number 2.
   When you send from your cellphone, these may go through ISP number 3. 

So, in summary, the following things affect the delivery of your email, and they are all outside of our (and your) control...

• SORBS generates blacklisting entries for IP addresses 
• It is your recipient's choice to use SORBS to filter incoming mail 
• Your IP address is changeable, so settling on a "clean" IP is not possible 

There is an appeals process to get your IP delisted. However, if your temporary IP was the one blacklisted, the chances are you'll be assigned a new IP before the current one gets delisted.

What can you do?

1. Ask us to confirm that this is the reason why your email was undelivered
2. Ask us to apply to have the IP address delisted