Hi I am interested in this. I did not know or had not heard of other folk having problems but I have wasted hours with one client using an iBook via Wireless with just the same problem. Mostly off but intermittent SMTP issue where no mail application will send. The iBook is / was keeping re-inventing settings deleted, underlining the beauty and simplicity of Classic Mac OS. [ try stripping things out of OS X it is as bad as Windows ... bits everywhere ] Port 25 is smtp, you cant/wont/should not change that. In my experience, it was not a problem with the router or the ISP's mail server. I could ping the smpt server and so reckoned the computer could see it fine. Last I left it after stripping any preference related and resetting it. Who knows if it will stick!? There are some automatic scripts in the Library to remove smtp mail settings, you need to remove any settings in the Internet control panel as well ... Who knows what is going on. Sometimes the error message related to the ISP not accepting a message being " relayed " via their server when it was plainly not being relayed just sent. How does OS X client work? Is it running its own mail server under the hood and the sending things on to the ISP? [ e.g. You write mail as user client and send it the OS's mail server that then sends it to the ISP's server? I could understand how if this screws up it could be related to relaying ] Could you forward any links to discussion that you have found? Thanks, John > I have seen coments on Apple's discussion boards regarding the last > upgrade to 10.2.8- > several people were having difficulty sending mail. Never read any > solutions though.