If everyone except one person in your address book is receiving your mail ok, then the problem would seem to be with the recipient's e-mail system. Does this person have a problem receiving mail from anyone other than you?

fwiw;
I deal with three seperate email accounts/companies. They have all started, withing the past month, new forms of sending server verification before accepting mail. Initially created problems for me - almost seemed like my email nearly completely stopped. I was self filtering my spam.

I know a part of what one actually does. It returns a server busy code with each new mail and then accepts the sending servers second try compairing or verifying the emails unique originating ID. Then on the sending server second try it runs the email through their spam check programs before putting it in my inbox.

Still has caused some of my email to not come at all or come hours later. Hopefully they'll get it fined tuned as time goes on.

Another thing you might try is checking the email if it gets returned to you as I assume it does. Right click on the header, click Properties/Details/Message source. Increase to full screen and look down through the gibberish. You may see SORBS and a web site listed or other spam filtering used by their internet provider. Read the reason and you will see it is not your mail but your server is allowing spam to go out from others so their provider is blocking everything from that server.

I had that problem for a long time, but it was just when I email to AOL email addys. Seems AOL identified my ISP as having spamming issues or something.

Is the one who can't receive from you possibly the one and only AOL addy?

Sue

Indeed, as Sue writes AOL can be a PIA for sure. My wife runs a red hat group and has some AOL customers in her address book. Mostly their mail gets delivered but too often all the AOL addressed mail gets returned. It is never some AOL addresses, either all get delivered or all get returned. Strange crowd.