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I wouldn't think so. If PHPMail were broke, then I'd be thinking these forums would be flooded with support requests. I use the SMTP option myself, but I imagine most sites would be using the PHPMail option. Is it just your ISP you cannot send to, or is it more widespread? The fact that you are able to send to Hotmail and Yahoo show that PHPMailer is working. Can you give some detais of your XOOPS environment (OS, PHP version, dedicated or shared hosting, etc)?