554 (mxgmx116) Nemesis ESMTP Service refused; IP address is block listedWhat does 554 Nemesis ESMTP IP address is block listed mean?
Nemesis is the proprietary mail server software developed by 1&1 Ionos (United Internet AG) and used to handle inbound mail for GMX, WEB.DE, mail.com, and 1&1 hosted domains. When Nemesis returns this rejection, your sending IP is on the Nemesis-internal block list. The list is populated by a combination of public DNSBLs (Spamhaus, Abusix), Ionos sensor data, and abuse reports from German and European users. The hostname prefix in parentheses (such as mxgmx116, mxeueus002) identifies which Nemesis MX instance returned the rejection but is not relevant to the fix.
Is this a soft or hard bounce?
Nemesis serves a significant share of German consumer email. A Nemesis block effectively cuts off delivery to the German consumer market until Ionos removes the listing.
Common causes
Marks-as-spam from GMX, WEB.DE, or mail.com users feed directly into the Nemesis block list.
Nemesis queries Spamhaus and Abusix. Listings on those zones often propagate into the internal block list.
Ionos maintains spam trap addresses across its consumer mailbox population. Hitting traps results in immediate listing.
Missing or misaligned SPF, DKIM, DMARC, or a HELO that does not match PTR feeds the negative score.
How to fix it
Look up your IP at Spamhaus, Abusix, and Barracuda. Clearing public listings often resolves the Nemesis block automatically within 24 to 48 hours.
Submit a delisting request through postmaster.web.de (which also handles GMX and mail.com). Provide your IP, sending domain, evidence of legitimate use, and a description of remediation taken.
Use email verification to remove invalid addresses. Add Nemesis to your blocklist monitoring if your tooling supports it.
Provider-specific notes
| Recipient domain | Operator notes |
|---|---|
| GMX.de, GMX.net, GMX.com | All routed through Nemesis. Same block list, same removal path through Ionos postmaster. |
| WEB.DE, freenet.de | Same Nemesis infrastructure. WEB.DE is the largest German consumer mail provider. |
| mail.com, 1and1.com, ionos.com | Mail.com is the global consumer brand. 1and1.com/ionos.com cover hosted business domains. |
Related error codes
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About the Author
Alaa · LinkedIn
Email infrastructure specialist with 8+ years of hands-on experience in SMTP, deliverability, and email verification. I’ve configured and troubleshot mail systems across Postfix, Exchange, and cloud relays, managed IP reputation and warmup campaigns, and built verification pipelines processing millions of addresses. My work spans DNS authentication (SPF, DKIM, DMARC, BIMI), bounce handling, blocklist monitoring, and compliance frameworks including CAN-SPAM and GDPR. I write every article on SMTPedia to give email professionals, developers, and marketers the accurate, RFC-grounded reference they need.
About SMTPedia
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