Ok, so I dont normally 'do' Mac repairs but this is and was a royal pain so I thought I'd be nice for those AppleFans out there. In fact this is so easy to sort yet it presents what I would describe as 'false' errors.
Mac Mini with Office 2008 connected by HTTP - No new emails arriving and everytime we click send it comes back with a HTTP error.
Well let me put your mind at ease first by telling you that its not a MAC problem, or an Office problem. In fact its a server issue. Now if your the troubleshooting type like me, you've probably whizzed onto the SBS ran "IISRESET", maybe checked Alias's, heck even reset the users password.
BUT did you check Licensing..? That's right it would seem that this is an error linked directly to Exchange not allowing any more connections. To test this, simply go into services and stop the "License Logging Service" the users mail will pop up and start working instantly. (Please enable this service again and only use this to test, disabling it is considered violation of Microsoft's Licensing Policies and will be upheld by them if they spot check you.)
So there is your resolution, you need to invest in some Small Business Server Cals :)
Did I solve your problem? Buy me a virtual beer by clicking on a Google ad :). Thanks!