Verifying GMX, WEB.DE and mail.com Addresses: Why They Come Back Risky

GMX, WEB.DE and mail.com addresses often come back risky because the providers refuse the mailbox check itself. In our October 2026 test of 51 consumer providers, gmx.com, gmx.de, web.de and mail.com all refused to talk to the checker, in both rounds ten hours apart. The reason shown is "Server refused our check". See the full table in how 51 mailbox providers answered a verification check.

If your list is a German or Austrian consumer list, expect a large risky bucket on these domains. Here is how to read it.

What "Server refused our check" means

The server declined to answer, so nothing about the mailbox was learned. A normal check connects, offers the address and reads the reply. Here the refusal came before that reply could tell us anything. That says more about how the provider judges the checking server than about the person's address. The result is risky because we have no confirmation, not because we found a fault.

Result	Reason	Your move
Risky	Server refused our check	Unconfirmed. Send only with care and a small test
Invalid	Mailbox not found	The provider said no. Remove it
Valid	Mailbox exists	Provider accepted it. Rare on these domains

What we can and cannot say

• We can say what happened in our test, on that day, from our server.
• We cannot say that the providers will do the same tomorrow or for another network.
• We cannot say which addresses on these domains are real.

Providers change their rules, so the behaviour is worth rechecking occasionally.

A safe way to send to these addresses

Treat the group as its own segment, not as a verdict. Pull the GMX, WEB.DE and mail.com addresses into a separate file. Prefer ones that you collected yourself, such as signups. Send a few hundred first and read the bounces. If you do see bounces, GMX and WEB.DE publish their own error messages: GMX and WEB.DE bounce messages explained. Remove any address that bounces as an unknown user.

For splitting a list by provider before you start, see routing leads by mail provider and how to tell which provider an email is on.

Why not just trust a "valid" from another tool

A confident valid on a provider that refuses probes deserves suspicion. If a tool marks every GMX address valid, it may be reporting a default, not an answer. Test a sample of its "valid" GMX addresses with a small send. Our approach is to say risky and give the reason, so you can decide with the facts. The wider question of what a verifier can honestly claim is in why most of my list is risky.

Check your list now

Run a sample on the verify page: the first 100 email checks are free with a Google sign-in, no card. Each comes back valid, risky or invalid with a reason, and nothing is sent to anyone on the list. For a bigger file, see bulk email verification, list cleaning and pricing.

For a single WEB.DE address, the free WEB.DE email checker shows the result and reason.