email send with php identified as phishing

Question

I've git a problem with an registration script of my login.

This script handles the registration information of the user and saves them. Additional an email is send to this person, in order to verify his emailaddress.

The problem is that this email is markes as a phishing email by thunderbird.

    //send verify email
    $sender = "test@example.de";
    $empfaenger = $email;
    $betreff = "Welcome";
    $mailtext = "Thank you for your registration.
    Please go to <a href=\"http://validatingsite.de\">this site</a> and enter your 
    activationcode in order to verify your email-address";

    mail($empfaenger, $betreff, $mailtext, "From: $sender\n" . "Content-Type:
    text/html; charset=iso-8859-1\n")

If I delete the link

<a> href=\"http://validatingsite.de\">this site</a>

the email is not marked and everything is okay.

Anybody an idea how to solve my problem? Do I add the link correctly in the email?

Answer 1

That's Thunderbird behaving as designed: https://support.mozillamessaging.com/en-US/kb/thunderbirds-scam-detection#w_thunderbirds-automatic-scam-filtering

Note the first bullet in their list of items that will trip the phishing detection: links with numerical server names (http://127.0.0.1/)