Today I received a request for help from a customer, together with screenshots. He wanted to open his email at gmx.net as usual, but the login failed.
GMX reported: “Login temporarily unavailable. Logging in from your current IP address 13.107.246.45 is currently not possible.” […] “Your IP address has been temporarily blocked because it accessed our website unusually often.”
I have, of course, replaced the real IP address in this article for privacy reasons.
What had happened? Had my customer sent a huge amount of spam? Had the laptop been hacked? Or was somebody else using the private Wi-Fi?
The detail that made the difference
For simplicity, let us call my customer “Erik”. He had already tried restarting the notebook, restarting the router and using Firefox instead of Google Chrome. None of these steps helped.
When I asked about his internet provider, the answer was Vodafone cable. That gave me an initial suspicion, but we still needed evidence. I asked Erik to check his public IP address using an IP-check website. It was “13.107.246.45”.
Next, he created a mobile hotspot on his smartphone and connected the laptop to it. The GMX login still failed. A second IP check again showed “13.107.246.45”. The smartphone was still connected to the home Wi-Fi and was simply sharing that connection through the hotspot. After Wi-Fi was disabled on the phone, the IP address changed to one from the mobile network and the GMX login worked again.
What caused the problem?
The cable connection was a residential connection. The public IPv4 address was not necessarily assigned to one customer alone; the provider could make one address available to many connections using carrier-grade address translation.
Public IPv4 addresses are limited. If unusual traffic from one participant causes GMX to block the shared address, other customers using that same address can temporarily lose access as well. The successful test through a different mobile connection strongly indicated that the block applied to the public IP address rather than to Erik’s GMX account.
What can I do?
- Use the smartphone’s mobile data temporarily.
A mobile hotspot can provide an alternative connection. Make sure Wi-Fi is disabled on the phone, watch the data allowance in your tariff and avoid data-heavy video services if the connection is needed for longer. - Disconnect the router from power for longer.
Depending on the provider and connection type, reconnecting after an extended interruption may result in a different public IP address. This is not guaranteed and provider behaviour can change. - Ask the provider about a dedicated public IPv4 address.
For business use or recurring problems, a tariff option with an individual address may be appropriate. Availability and pricing must be confirmed with the provider.
What if the problem remains?
If the message still appears through a different internet connection, or if you already use a dedicated address, another cause is more likely:
- The device may be infected with malware and the GMX account may have been abused to send spam. Check the device with current security software before asking GMX to unlock the account, and change credentials only from a trusted, clean device.
- The account may genuinely have sent an unusually large number of messages. Consumer mailboxes are not suitable for newsletters or bulk distribution; use a professional mail or newsletter service for that purpose.
More information from BITSS: Email security for businesses · IT security check