You should currently be alert if an email of unknown origin from a gmx domain lands in your inbox.
Often, these emails contain short links such as bit.ly, behind which, for example, advertising websites with software freely available for download are hidden. Both clicking on the link and downloading the software can infect your computer with possible malware.
Since it is not possible to block gmx addresses or bit.ly links in general for obvious reasons, you should be particularly vigilant with regard to the sender of your emails. If you do not know the sender at all, you should ideally delete the message directly without opening it.
You can find more information on the topic of phishing on our IT security websites.