First of all, let me point out that the title (and content of this article) does not read out “GMX is evil”. I like GMX, but imho they made a mistake in enabling @gmx.net as a possible domain part in their free email service.

GMX (short for Global Message eXchange) was founded as a German company and is now owned by United Internet. The most popular service back in the days (and maybe still today) was their freemail service.

When users registered an email account with their service, they could choose an individual local-part of the email address and choose from a list of domain-parts (because GMX owned several domains).
The earliest choices I do remember were gmx.de, gmx.com and gmx.net – later on they added domains like gmx.at and gmx.li (even though I have to admit, the very beginning in 1997 might have been just gmx.de, as I wasn’t using their service back then). The list grew bigger with other TLDs and various new domain names.

But to cut to the chase: whereas practically all TLDs are localized and therefore bare a certain mark (in addition to .com carrying the stigma of being special), .net has undefined attributes. My guess is, people decided to use @gmx.net because they didn’t want to use .com with a German email account (because back then .com equaled English in our minds) or when desired email addresses were already taken with @gmx.de .
However, the main problem with @gmx.net was that in our minds there weren’t enough characteristics to longterm differentiate it from @gmx.de . After a while people forgot whether an email address used @gmx.net or @gmx.de (maybe not their own but pretty much every other email address that wasn’t in an address book).
The first email address I registered with GMX (and one I’m still primarily using for private contacts) ended in @gmx.de – the local-part is very easy to remember and I thought people might actually remember the email address without having to write it down. I have since then encountered a myriad of occasions when people asked me if my email was @gmx.de or @gmx.net! It even got to the point where people wrote emails to @gmx.net because they could only remember the local-part. That’s when I also registered the same local-part but with @gmx.net . The effect is, I actually do get all emails intended for me – but people still ask me the evil question.

That said, I still like using GMX and considering the fact that many people actually do remember this very old address by heart I would never give it up. However, it’s not only sort of annoying to be asked about the domain-part, but I’m just angry at GMX for ever having created that domain choice :).