Retarus (DE gateway) email service provider (ESP)
According to Live Direct Marketing's daily Tranco top-1M scan (September 22, 2026), Retarus (DE gateway) is the email service provider (ESP) for 189 domains — 0.03% of 637,585 SPF-publishing domains. Detection method: include: mechanisms in the SPF record.
Key facts
- 189 domains in the Tranco top-1M use Retarus (DE gateway) (0.03% of SPF-publishing domains).
- Snapshot date: 2026-09-22 — recomputed every day.
- Strongest TLD: .de (38.6% of its domains).
- Most co-used service: Retarus.
- Directory category: email security gateway.
Why Retarus (DE gateway) appears in this category
Munich enterprise messaging gateway (transactional + secure email).
We classify it as a email security gateway from include: mechanisms in the SPF record matching a maintained provider rule. This is infrastructure attribution from public DNS, not evidence of a direct contract or exclusive use.
Retarus is a German email service provider specialising in managed SMTP gateways and message relay infrastructure. The company operates email delivery platforms serving organisations across Europe and internationally, providing services including message relay, security filtering, and archiving through its gateway network.
Retarus appears frequently in SPF authentication mechanisms across the web, indicating that many organisations have delegated their outbound mail relay to Retarus's infrastructure. The provider's footprint concentrates in the mid-market and small-to-medium business segment rather than amongst the largest global enterprises, with particularly strong adoption across German-language domains (.de) and other European top-level domains, reflecting its primary geographic market.
Where Retarus (DE gateway) sits in the Tranco ranking
| Tranco rank band | Domains | Share of its base |
|---|---|---|
| Top 1,000 | 0 | 0.0% |
| Top 10,000 | 3 | 1.6% |
| Top 100,000 | 30 | 15.9% |
| Top 1,000,000 | 156 | 82.5% |
| Unranked | 0 | 0.0% |
Top-level domain split
| TLD | Domains | Share | |
|---|---|---|---|
| .de | 73 | 38.6% | |
| .com | 59 | 31.2% | |
| .fr | 10 | 5.3% | |
| .ch | 8 | 4.2% | |
| .it | 5 | 2.6% | |
| .at | 5 | 2.6% | |
| .es | 4 | 2.1% | |
| .nl | 3 | 1.6% | |
| .eu | 2 | 1.1% | |
| .pl | 2 | 1.1% |
What Retarus (DE gateway) users also use
Cross-tabulated from the same daily snapshot — the other email services seen on the same 189 domains.
| Type | Service | Domains | Share of Retarus (DE gateway) users |
|---|---|---|---|
| Mailbox | Retarus | 87 | 46.0% |
| Mailbox | Microsoft 365 | 65 | 34.4% |
| Mailbox | Self-Hosted | 11 | 5.8% |
| Mailbox | Proofpoint | 6 | 3.2% |
| Mailbox | Google Workspace | 4 | 2.1% |
| Mailbox | Generic / unmatched (mx*.*) | 4 | 2.1% |
| ESP | IP Made (CDP) | 30 | 15.9% |
| ESP | Mailgun | 19 | 10.1% |
| ESP | Salesforce | 13 | 6.9% |
| ESP | Mailchimp | 12 | 6.3% |
Retarus relays and shared infrastructure reputation
Because Retarus operates as a shared gateway platform for many customers, sender reputation at Retarus's IP addresses is pooled across the relay's entire customer base. Mail receivers that track IP reputation will associate inbound traffic from Retarus relays with the aggregate sending behaviour of all Retarus customers, not just an individual sender. This means that a deliverability issue affecting one Retarus customer—such as complaint spikes or sending to invalid addresses—can degrade message acceptance rates across other customers using the same relay addresses.
See the full Retarus (DE gateway) data page (KPI cards, trend, sample domains) →
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Frequently asked questions
What is Retarus and why does it appear in SPF records?
Retarus is a German email gateway and managed relay provider that handles outbound SMTP traffic for many mid-market organisations. You will see Retarus's SPF include mechanisms in domains where the organisation has delegated their mail delivery to Retarus's infrastructure.
How many domains use Retarus (DE gateway)?
189 domains in the Tranco top-1M use Retarus (DE gateway) as their email service provider (ESP) as of September 22, 2026 (0.03% of SPF-publishing domains), according to Live Direct Marketing's daily DNS scan.
Is Retarus (DE gateway) common enough to affect email deliverability testing?
Retarus (DE gateway) accounts for 0.03% of SPF-publishing domains in the top 1M. Whether you should seed a test mailbox there depends on how much of your audience it represents — the co-usage table above shows the services it appears alongside most.
Which countries or TLDs use Retarus (DE gateway) most?
Retarus (DE gateway)'s largest TLD is .de (38.6% of its domains); it appears across 26 TLDs in total.