Over the last week over a dozen sent e-mails have disappeared into Cyberspace. In reviewing my logs, I see that my IP has been blacklisted by spamhaus XBL and cbl.abuseat.org. I have corrected with these orgamizations already. CBL says "it happened for a reason - fix it". Is there something is our e-mail server that could be relaying or other items that could be responsible for this. All incoming and outgoing e-mails are scanned by AVG and should be good. Some other source??

A really troubling thing is that we go no bounces, so we never knew we had this problem. CBL log says "could not get return IP address". Is this in my server control or any options??

We cannot rely on our outgoing e-mails being received, and are requesting read receipts on everything.

Mail servers generally do not bounce back messages that come from  a blacklisted server.  The premise is that All spam is forged. Which means that every spam that gets bounced will probably hit an innocent third party who had nothing to do with it. This is called "backscatter". It's spam. It's part of the spam problem, not part of the spam solution. The ability to let a legitimate non-spamming sender know that their email was blocked without causing backscatter has been well known issue for years.  CBL should have given a reason on why you were blacklisted   With that information we can help identify the problem and point you in the right direction to correct it. 

The CBL takes its source data from very large spamtraps/mail infrastructures, and only lists IPs exhibiting characteristics which are specific to open proxies of various sorts (HTTP, socks, AnalogX, wingate etc) and dedicated Spam BOTs which have been abused to send spam, worms/viruses that do their own direct mail transmission, or some types of trojan-horse or "stealth" spamware, dictionary mail harvesters etc.

More info on the CBL can be found here at http://cbl.abuseat.org/