GMX how to configure?

I see a discussion that some must use gmx.net ...so, try... pop.gmx.net

You should not use pop.
Just www.gmx.[net/com/fr].
And the www is optional.

Did you read http://xnotifier.tobwithu.com/dp/node/4 ?
Follow the guidelines and you should be ok.

That is the reason the Xnotifier script gets blocked.
Sometimes mail servers give you all kind of warning pages after login, where you have to click a button to get forwarded to the inbox page. Normally you should login manually and make that warning page disappear, because the Xnotifier script cannot know what warning page your mail provider comes up with next. But when this page is part of a standard scenario of the mail server's login procedure, like in this case having to logout after a session, the problem can only be resolved (by tobwithu) thru a logout and re-login fix in the Xnotifier script.

Am I correct, RpD / tobwithu?

After having a look at the gmx.com  script I see it already is prepared for the logout reminder page. So... I was wrong. It is probably not the reason your login is failing, because you are the only one having a problem (I don't have a gmx account).

So, back to the troubleshooting post.
(You might start by re-entering your gmx password in the X-notifier Options window. Don't forget to click the Ok button after that)

[EDIT:  The mail.com script can accommodate the 'forgot to logout' reminder and still check for email.]

GMX bought mail.com and then I started getting that damn logout reminder if I didn't click the 'Log out' button... [I tested three accounts and] it does NOT interfere with X-Notifier checking for new email.  Any time I forget to click 'Log out' (or just close the browser or power fails...while I have mail.com inbox open), I have to go back later, open a new tab, go to www.mail.com, sign in, and click the "Continue to Inbox" button... and then "Log out" ...[to get rid of that darn logout reminder]... but it does NOT matter to the mail.com script for checking of email.

 So I'm retracting my earlier statement that it did interfere ...oh well.

The mail.com script also contains that code, so perhaps it really does need a fix?

 <code>
    case ST_LOGIN_RES:
    var fnd=aData.match(/tryToProceedDirectly[\s\S]+?(http\S+?)'/);
    if(fnd){
      this.navigator=true;
      this.viewURL=fnd[1].replace(/remindlogout/,"show");
      this.getHtml(this.viewURL);
      return false;
    }
</code>

and...

<code>
  case ST_LOGIN_RES+1:
    var fnd=aData.match(/"logout_url":"((\S+?)logout(\?sid=\S+?))"/);
    if(fnd){
      fnd[2]=fnd[2].replace(/\\/g,"");
      this.logoutURL=fnd[1].replace(/\\/g,"");
      this.dataURL=fnd[2].replace(/\/\//,"\/\/home.")+"servicetrinity/mails"+fnd[3];
      this.stage=ST_DATA;
    }
</code>

[EDIT:   I tested my accounts and the mail.com script -does- handle the 'forgot to logout' reminder... so I'm not sure what is causing a problem for Owned with the gmx.com script.]

Obviously the "Allowed HTML tags", like <code>, are not working here. Also I have to keep entering the Captcha numerous times to post. Grrrr...

When you really get bored of it, RpD ;-) , you might have a look at the html of that 'reminder' page yourself and check if the text, the script code is looking for and trying to replace in forming the proceeding or logout url (check what it should be in the <form> of the logout button), has changed (f.i. tryToProceedDirectly, remindlogout, logout_url, servicetrinity/mails). Sometimes the solution is easy to spot. You might get lucky :-)

Hey... I edited my posts above because I tested my mail.com script by not logging out and forcing the logout reminder screen on my three mail.com accounts. Sent myself some emails and X-Notifier checked and found them all even though there were logout reminders set to display during the login process.  After X-Notifier checks, I verified that occurred... so I expect that it's not a problem on the GMX script either, but I don't have any gmx accounts.  Don't know what's causing a problem for Owned.  My X-Notifier checks and see new emails even when I have forced that logout reminder (by not logging out but closing the browser).