Not Getting any Replies?

One thing I apologize for, is that I'm not always able to keep up with my correspondence. This is because I'm a software engineer, which is a horribly hectic occupation. Please have faith, and know that I do go back and try to catch up with my email from time to time. But sometimes even when I do reply, I get the following result:

AOL Users Please Note if you send a mail to me and get no reply, it may be because you have blocked the domain "geometricvisions.com" from sending you mail, or you may have configured your mail preferences to only accept mail from particular people, without including me.

Sometimes AOL users send me urgent questions, but I cannot reply. When I try I get bounced mail like the following:

   ----- The following addresses had permanent fatal errors -----
xxxxxx@aol.com

   ----- Transcript of session follows -----
... while talking to air-zd05.mail.aol.com.:
>>> RCPT To:xxxxxx@aol.com
<<< 550 xxxxxx IS NOT ACCEPTING MAIL FROM THIS SENDER
550 xxxxxx@aol.com... User unknown

   ----- Original message follows -----