554 5.7.1 — Client host blocked (GMX / Web.de)
PermanentReputation
Retrying will not help. The message will not be delivered.
The reply
554 5.7.1 Service unavailable; Client host blocked.Your sending IP is blocked. GMX consults public blocklists heavily, so the first check is Spamhaus — and unlike a reputation problem at Gmail, a listing here is concrete and removable.
What it means
A permanent rejection at connection or policy level. United Internet's filtering gives public blocklist status real weight, which makes this one of the more tractable blocks: there is usually a specific listing to find and a specific delisting process to follow.
Why it happens
- The IP is listed on Spamhaus, Barracuda, SpamCop or a similar public list.
- No reverse DNS on the sending IP, or a PTR that does not match the HELO name.
- A new IP in a range associated with abuse.
- Complaints from GMX or Web.de users about earlier mail.
What to do
- Check the IP on Spamhaus ZEN first — it is the likeliest single cause and it has a self-service delisting process.
- Set forward-confirmed reverse DNS and make the HELO name match it.
- Publish SPF, DKIM and DMARC.
- Once every listing is cleared, contact GMX support with the IP and the exact reply.
- Ramp volume gradually rather than resuming at the previous rate.
Questions
Google accepts my mail from the same IP.
Google runs its own reputation system and largely ignores public blocklists. GMX does not, so a Spamhaus listing that Gmail overlooks will block you here. Check the listings first.