Three channels. Pick the right one.
We route inbound by intent rather than dump everything into a single contact form. If you are pricing a new account, you talk to sales. If you are architecting a migration or have a specific technical question, you book a 45-minute call with an actual engineer — not pre-sales. If you are already a customer with an operational problem, you go to support and we route by your plan tier. The exact emails, phone extensions, and guaranteed response times for each channel are below.
- Closest metro
- Stephansplatz U1/U3 · 4 minutes walk
- Visits
- By appointment only. We are an operating team, not a public showroom — schedule with sales@ first. Visitor badge required at reception.
Each channel has its own people, its own response times, and its own escalation path.
Sales
Quotes, new accounts, plan changes, migration estimates.
- [email protected]
- Phone
- +43 1 205 11 80
- Hours
- Mon–Fri · 9–18 CET
- Response
- 2 business hours during EU hours · 8h otherwise
When to use this channel
- Picking the right plan for your volume
- Custom Enterprise quote (BYOIP, ASN delegation, on-prem hybrid)
- Migration scoping from SES, SendGrid, Mailgun, SparkPost, Postmark
- Discount eligibility (non-profit, startup, annual prepayment)
- Invoicing, payment terms, NDA before pricing discussion
Engineering
45-minute architecture calls. Real engineers, not pre-sales.
- [email protected]
- Phone
- +43 1 205 11 80 ext. 2
- Hours
- Tue–Thu · 13–17 CET (booked slots)
- Response
- Bookable within 3 business days
When to use this channel
- How to migrate without breaking your existing send reputation
- PowerMTA vs KumoMTA — which suits your traffic pattern
- IP warm-up strategy for a new domain or vertical
- DMARC enforcement rollout from p=none to p=reject
- Custom integration with your CRM, marketing automation, or transactional service
Customer support
For existing customers. Operational issues, deliverability help.
- [email protected]
- Phone
- +43 1 205 11 80 ext. 3
- Hours
- Tier-dependent — see response table below
- Response
- Starter 24h · Standard 8h · Performance 1h · Enterprise contractual
When to use this channel
- Specific IP showing up on a blocklist
- Gmail/Outlook/Yahoo postmaster anomalies
- Webhook signing verification failing
- Bounce-rate spike investigation
- API rate-limit increase request
Customer-support response is tier-dependent. Sales and engineering are tier-agnostic.
Once you are a customer, the response time to support tickets and phone calls depends on your plan. Sales and engineering response times above are the same regardless of whether you are on Starter or Enterprise — we are not going to make a prospective customer wait three days because they have not bought yet.
| Plan | Standard support | Emergency / incident | SLA |
|---|---|---|---|
| Starter | Email · weekday 24h | No phone after hours | 99.9% uptime · service credit |
| Standard | Email · 8h · phone EU hours | No phone after hours · Slack opt-in | 99.95% uptime · service credit |
| Performance | 24/7 phone + dedicated Slack channel | 1h response · pager rotation | 99.99% uptime · service credit + RCA |
| Enterprise | 24/7 named CSM + war-room call | 30-min response · cash refunds above contractual threshold | Custom · NDA |
If you would rather email than call.
We route by the "Topic" field below — that determines which inbox the message lands in and who acks first. Honest answer: messages with a clear topic and a concrete question get faster, better responses. Vague "let's hop on a quick call to discuss synergies" emails get filed.
Privacy: what you send here goes to our customer-service inbox hosted on our own infrastructure (eat-your-own-dogfood policy). We do not load this form to a CRM that resells data, and we do not use form metadata for retargeting ads.
Journalists, podcasts, conferences
We respond to press inquiries within 1 business day during EU hours. Our CEO is available for interviews on email infrastructure, DMARC enforcement, Schrems II and EU data sovereignty, and the economics of running email infrastructure on owned bare-metal versus hyperscaler API products. Background: we have been operating since 2008, are self-funded (no VC), and our team has previously been at Sendinblue, Postmark, and various ESPs.
- Email:
- [email protected]
- Press kit:
- Logos, headshots, fact sheet on request
- Spokespeople:
- CEO, CTO, Head of Deliverability (EN/DE/FR)
We are not raising, but we are reachable
OS Domains GmbH is profitable, self-funded, and has not taken outside capital since founding in 2008. We have no plans to raise. If you represent a strategic investor or industry consolidator (PE rolling up European hosting, ESP looking for infrastructure acquisition, telco looking for email-deliverability stack), we will respond to a serious approach with a 30-minute exploratory call. Cold outreach about partnership/acquisition that doesn't fit those buckets gets a polite "no thanks, focus is on the business."
- Email:
- [email protected]
- Last update:
- Annual letter to stakeholders published in January
Responsible disclosure program
If you have found a security vulnerability in our infrastructure, customer portal, or API, please disclose responsibly. We acknowledge within 24 hours, triage within 5 business days, and credit you in the security changelog once the issue is patched. We do not have a paid bounty program — we are a small operating team, not a hyperscaler — but serious findings are rewarded with merchandise, a public credit, and a thank-you letter. The PGP key for encrypted reports is published on our security.txt file.
- Email:
- [email protected]
Five things people ask before reaching out.
01 Will my message get a salesperson on commission?
No. Our sales team is on salary plus a small annual performance bonus tied to customer retention rather than new-deal commission. That means nobody is incentivized to push you into a larger plan than you need or close before you are ready. If the answer to your inquiry is "you should stay on AWS SES, you are too small for us," you will hear that.
02 Do I have to fill out a "discovery questionnaire" before getting a price?
No. Starter, Standard, and Performance prices are on the pricing page. Enterprise pricing requires a call because the deployment is custom (BYOIP, ASN, hybrid), not because we want to qualify you. The architecture call is 45 minutes with an engineer (not a salesperson), and you walk away with a written quote within 5 business days regardless of whether you proceed.
03 Can I visit your office in Vienna?
Yes, by appointment. Email [email protected] at least 1 week in advance. We are an operating team in a working office, not a public reception with marketing displays, so drop-ins do not work — there is usually nobody at the door to greet visitors. For Enterprise customers we host architecture workshops and quarterly business reviews in person.
04 What if my issue is urgent and I'm not yet a customer?
If you are in active email crisis (provider went down, IPs blacklisted, deliverability dropped overnight) and considering a fast migration, write to [email protected] with "URGENT" in the subject. We have a same-day onboarding path for crises that includes a 30-minute call with an engineer within 4 hours. The deliverability audit service can also start same-day in those situations.
05 In what languages can you respond?
English, German, Spanish, Portuguese (Brazilian), and French. Italian and Dutch via async email but not phone. Default working language for engineering discussions is English because that is how the documentation, RFCs, and ISP postmaster channels work; we can switch to your local language for sales and customer-success conversations.
Call, write, or skip the talk and order online.
Phone is faster for sales questions and emergencies. Email is faster for technical specs and quotes. Self-serve is fastest if you already know which plan you want — go to pricing, complete the order form, we provision in 48-72 hours.