<blockquote> My ISP insists the problem is not with their server </blockquote> <blockquote> An error occurred while sending mail. The mail server responded: Spam detected by content scanner. Message rejected (ID 665754780026FB52). </blockquote> The error message '''is''' from your ISPs mail server. So they are the one causing the problem for you. <blockquote> I need to have Mozilla correct it. </blockquote> There is nothing Mozilla can do about it. What you could try though is * send email in plain text instead of HTML * don't use any linked files in your email signature * avoid attachments None of that will actually solve the underlying problem. It's just an attempt to work around an overly sensible spam detection mechanism your ISP has implemented which generates false positives for you. Another workaround may be to use webmail to send those problematic messages.