| GMX | |
|---|---|
| Domains | gmx.com, gmx.de, gmx.net, gmx.at, gmx.ch |
| Mail routing | mx00.emig.gmx.net and mx01.emig.gmx.net for gmx.de, gmx.net, gmx.at and gmx.ch, measured in September 2026. gmx.com listed mx00.gmx.net and mx01.gmx.net. All of it shares an operator with Web.de. |
| What we can resolve | We resolve most mailboxes here |
How GMX answers a probe
What the server does when we open a connection and ask about one address.
- Unknown local parts get a 550 with a Requested action not taken message. The answer is reliable.
- Connection limits are strict and enforced per IP, so a burst of probes earns a temporary block that lasts long enough to matter.
- GMX and Web.de share an operator, and probing patterns that annoy one will annoy the other.
- Non-ASCII local parts appear more often on German consumer lists than on English-language ones, and umlauts in an address are a routine source of encoding bugs before the probe even runs.
The part that catches people out
What we do about it
We pace probes to GMX ranges to stay inside their limits and report mailboxes normally. We do not attempt to infer whether an account is dormant, because that is one of the things no SMTP check can establish.
Sending to GMX mailboxes
Verification is one step. These are the things that decide whether the message lands.
- German recipients bring GDPR consent expectations that are stricter in practice than the regulation's text suggests. Documented opt-in matters.
- United Internet's filtering reacts quickly to complaint volume, and reputation recovery is slower than at Gmail.
- A German consumer list without GMX and Web.de addresses is probably incomplete, so their absence is a sourcing signal worth checking.
gmx.com and gmx.de are not the same door
Check the MX records and the two split apart. On September 19, 2026, gmx.de, gmx.net, gmx.at and gmx.ch all listed mx00.emig.gmx.net and mx01.emig.gmx.net. gmx.com listed mx00.gmx.net and mx01.gmx.net, without the emig label, which almost certainly refers to the E-Mail made in Germany program that GMX, Web.de and Telekom announced in 2013. The .com service is the international arm, and its sibling is mail.com, whose mail hosts are mx00.mail.com and mx01.mail.com.
mail.com is where it gets interesting for list cleaning. It hands out addresses on a long menu of vanity domains, and email.com and usa.com both returned the mail.com MX in our lookup. So say you find 35 rows at usa.com on a US list. Those are real mailboxes run by the same operator as GMX, and they should share whatever pacing you apply to it.
A 554 before you've said anything
Two refusals from this operator look alike in a log and mean opposite things. A 550 after RCPT TO is about the mailbox. The 554 that arrives with the greeting, before any recipient has been named, is about the connecting IP. United Internet's servers identify themselves as Nemesis ESMTP, and when they don't like the address you're calling from, the banner itself says the service isn't available to you.
Ask a vendor which of those two they count as invalid. If the answer is both, every gmx.de row probed on a bad day gets deleted for something that had nothing to do with the address. We mark the greeting-stage refusal as unknown, name the cause, and don't bill it. You can tell the difference in your own bounce logs the same way: look at which command the error followed.
Questions people ask
Can GMX addresses be verified?
Yes. GMX rejects unknown recipients with a standard 550 and does not run an anti-enumeration accept-all policy. The constraint is throughput rather than truthfulness.
Are GMX and Web.de the same service?
They share an owner, United Internet, and much of the same infrastructure. They are separate brands with separate user bases, and they behave almost identically when probed.
Why do old GMX addresses still accept mail?
Because free accounts are rarely deleted. An address created in 2003 will keep returning 250 whether or not anyone has read it since. That is a reachability problem, not a validity one.