What product? What letter? What service? Who are you? Solve what?

Sorry. Product http://callbackkiller.com Image in attach

Does your email message contain links to streamwood.ru as your website does?

Links to other sites often trigger Thunderbird's scam detection.

The source code used by the phishingDetector is here http://mxr.mozilla.org/comm-central/source/mail/base/content/phishingDetector.js

If you are not familiar with JavaScript you might have someone who is.

If he link node contains a user visible url with a host name that differs from the actual href the user would get taken to.. i.e. <a href="http://myevilsite.com">http://mozilla.org</a> This is the most common reason mails get incorrectly flags as marketers try and determine all sorts of metrics from their mail by redirecting the links to something other thn the advertised link