GMX, Web.de and T-Online: deliverability for the German audience

Ask a Western deliverability consultant about Germany and most will tell you about Gmail and Outlook. That is the reflex, and it is wrong. In Germany, Gmail is a minority provider. The mailboxes German consumers actually use are GMX, Web.de and T-Online — and those three ISPs have filters, postmaster portals, and authentication expectations that do not look like anything in the Gmail-centric playbook.

Germany's ISP share

German consumer mail splits roughly like this (2025 MAU data, rounded):

• GMX + Web.de — ~35% combined. Both owned by United Internet (1&1). Separate brands, shared MX and shared filter.
• T-Online — ~20%. Owned by Deutsche Telekom. Completely separate infrastructure and postmaster process.
• Gmail + Google Workspace — ~20%. Dominant for B2B tech, minority for consumer.
• Outlook.com + Microsoft 365 — ~10%. Dominant for German enterprise, minor for consumer.
• Other — Freenet, Strato, Arcor, Yahoo, iCloud, custom corporate — the remaining ~15%.

For a consumer B2C campaign in Germany, this means more than half your recipients are on ISPs that most of the industry does not measure. A Gmail-focused "90% inbox" report might be masking a 40% actual inbox rate on the majority of the list.

GMX and Web.de: one company, one filter

GMX and Web.de are both brands of United Internet / 1&1. They share MX servers and the same filtering stack, so placement on one is an excellent proxy for the other. The filter itself:

• Rules-based core with a layered Bayesian classifier. Newer than Rambler's legacy stack, older-school than Gmail's.
• Heavy weight on Cloudmark reputation. United Internet feeds user-reported spam directly into the Cloudmark Sender Intelligence platform, and uses the reputation output as a primary signal.
• Strict on subject-line content. Promotional patterns, all-caps, and certain German trigger phrases ("gratis", "kostenlos" in combination with urgency words) still score hard.
• Intolerant of HTML-only messages. A missing plain-text part is a much bigger deal here than at Gmail.

The Cloudmark connection

The postmaster portal for GMX/Web.de is effectively Cloudmark's portal at csi.cloudmark.com. You register your sending domain there, enrol in the feedback loop, and receive complaint reports. If Cloudmark has tagged you from other ISPs (e.g. Virgin Media, Vodafone) that reputation carries over to GMX/Web.de directly.

T-Online / Deutsche Telekom specifics

T-Online runs its own stack, separate from Cloudmark. It is the strictest of the three German ISPs on authentication and arguably the strictest major European provider overall. Notable characteristics:

• Greylist by default. First connection from a new sending IP is refused with 421 greylisted and must retry after ~5 minutes. Half-decent senders handle this natively; some cold-email tools do not.
• Strict DMARC. T-Online honours DMARC fully and movesp=quarantine mail to Spam aggressively. Alignment mode matters — relaxed vs strict changes placement outcomes.
• Image:text ratio enforcement. Messages above ~60% image area are scored down harshly. Holiday/promotional templates that pass Gmail fail T-Online routinely.
• URL reputation. T-Online consults SURBL and URIBL in-line on every message. A single blacklisted link anywhere in the body is usually fatal.

T-Online Sender Support

Deutsche Telekom runs a postmaster portal at postmaster.t-online.de (redirects to Sender Support). Registration is free but requires German-language forms and a verifiable abuse contact. Once registered you can submit for the T-Online whitelist after 60 days of clean sending — notably slower than Mail.ru's 30 days or Gmail's reputation-based model.

Authentication strictness in Germany

All three major German ISPs require valid SPF and DKIM. DMARC is honoured across the board. Specific numbers that matter:

• DKIM key length: 1024 minimum, 2048 recommended. T-Online slightly penalises 1024; GMX does not.
• SPF policy: -all is strongly preferred over ~all at all three. Soft-fail is accepted but scored lower.
• Alignment: relaxed DMARC alignment (adkim=r, aspf=r) is fine for GMX/Web.de. T-Online weighs strict alignment higher — move to adkim=s when your DKIM-From alignment is clean.
• MTA-STS and DANE: increasingly checked. Publishing an MTA-STS policy is a positive signal at T-Online specifically.

Typical rejection reasons

The SMTP-level rejection codes German ISPs return are unusually informative compared with American providers. Pay attention to them:

• 421 greylisted; try again in 300 seconds — T-Online first-contact. Retry and it delivers.
• 550 Message rejected; Cloudmark reputation — GMX/Web.de, you are on the Cloudmark bad list. Check csi.cloudmark.com.
• 550 5.7.1 Message rejected due to DMARC policy — DMARC failure at any of the three.
• 550 Message contains URL on SURBL — T-Online specifically, one of your links is blacklisted.
• 550 Image to text ratio too high — GMX/Web.de content rule tripped.

GDPR and German list-hygiene specifics

Germany enforces GDPR more strictly than most EU jurisdictions, and the Telemediengesetz adds a second layer specifically for electronic marketing. Practical consequences for deliverability:

• Opt-in documentation. German ISPs pay attention to consumer complaints, and complainants often cite "I never opted in". Keep opt-in timestamps and source URLs on every address. When a complaint reaches the ISP via FBL, the first defence you have is documented consent.
• Double opt-in is not legally mandatory but is effectively required for good reputation. Single opt-in in Germany produces complaint rates 3–5× higher than DOI, and GMX/T-Online are tuned to punish that.
• Right to erasure. Honour unsubscribe inside 72 hours, and purge permanently inside 30 days. ISPs do not verify this, but the complaint mechanics downstream are different if the same user complains twice.
• Impressum. Every bulk email to German consumers must contain a valid Impressum (legal footer with company details). Missing it triggers regulatory complaints that often reach ISPs before they reach you.

Setup order for the German market

1. Publish SPF with -all, DKIM at 2048 bits, DMARC starting at p=quarantine.
2. Register at Cloudmark CSI (covers GMX + Web.de).
3. Register at T-Online Sender Support.
4. Send a baseline seed test — confirm Inbox placement across all three.
5. Warm for 4 weeks. Start at 100/day to German recipients, double every 4 days.
6. After 30 days of clean sending, move DMARC to p=reject. After 60 days submit for the T-Online whitelist review.

Frequently asked questions