Eugene's observations

I'm sometimes asked why a client's messages are rejected or bounced by one or two recipients.

We all have an address on the internet ? that is how an email message knows where to go.  The problem is that when a suspected spammer or other person with nefarious intent has been traced back to his address, that address gets blacklisted on several lists to prevent more spam being sent.   A selection of these blacklists are checked my most email providers to ensure they are not responsible for propagating rubbish.

 Because there are more potentially internet connectable devices in the world than available addresses stale connections are dropped and when a new connection is requested a new address gets allocated.  You have been unfortunate to have picked up the address that the bad person used.

 There are ways of having it removed from the various blacklists but the time and effort involved is far more than the alternative method of resolution.  Visit  http://www.whatsmyip.org/  and make a note of the IP address on the top line.  Now power off your computer and any other internet connected devices including the router.   Count to 10 then power up the router.  After a minute power up your computer and any other devices you want.  Now visit  http://www.whatsmyip.org/  and see if your IP address has changed.  If so, send you email again and expect it to arrive.  If the address is the same, go through the above process again but wait much longer before powering up the router - overnight perhaps.

The above works for the 95% of people who have dynamic IP addresses allocated by their ISP.  If you have a static IP address (usually bought if you are a business hosting a server) then the above won't work; in that case you need to either get a new IP address issued by contacting your provider, or go through the process of proving to all the blacklist owners that you are not a bad person.