Retarus

What Retarus Transactional Email is

Retarus Transactional Email is an enterprise service for the email that business applications send on their own, from SAP systems to CRM and e-commerce software. The product page is headed "Enterprise Email Sending API by Developers, for Developers" and says any type of application can connect "via a REST or SMTP" interface. Retarus is a messaging company whose copyright line runs from 1992, and email is one product among several: it also sells cloud fax, enterprise SMS, email security, and business process services such as e-invoicing. The site is published in English, German, Spanish, French and Italian, and a press release on the home page says Retarus was named one of "Bavaria's Best 50" for the fourth time. The home page slogan for its email products is "Designed for Security. Made in Europe. Built for You."

This is not a newsletter tool. There is no campaign editor or subscriber list on the pages; the service is the delivery layer behind a company's own systems, run for IT teams.

Throughput and delivery commitments

Capacity is the headline. The product page gives "Up to 10 million emails per hour capacity" and a "Permanently high, guaranteed throughput rate", with "Global availability and local processing." Further down, it states a "Delivery rate of 98%+ far above market average, guaranteed processing capacity of 100K emails per hour. All contractually agreed." On reputation, it claims an average sender score of 99 against an industry average of 85. These are the company's own figures, and the phrase "contractually agreed" is the useful part for a buyer: the throughput and delivery numbers are written into the contract rather than left as marketing.

Smart throughput adjustment adapts sending behavior automatically to the requirements of each ISP and mailbox provider and, in the page's words, actively minimizes blocklist risk. Dynamic IP routing by sender domain is part of the same reputation toolkit.

Sending options

Applications submit mail over REST or SMTP, in JSON or SMTP/MIME format. The service supports sender IP authentication, IP allowlisting (so only named applications in the customer's network can use it) and multi-client setups, which the page ties to multi-domain configuration with failover and load balancing options. Retarus supports both IPv4 and IPv6.

A Destination Relay feature sends mail to a custom target server instead of the recipient's domain. Sender address rewriting changes the envelope from-address on outgoing mail, so that internal company domains are not used for external communication and replies can be routed straight to a dedicated inbox. Attachments can be encrypted, a service Retarus offers together with its AntiVirus MultiScan. TLS encryption is enforced based on the sender domain.

Reputation, authentication and dedicated IPs

The reputation section lists SPF, DKIM and DMARC, blocklist monitoring, a registered sender domain and CSA certification. Retarus offers IPs certified by the Certified Senders Alliance that are ready to use, and supports the warm-up phase when a customer moves to a dedicated IP. For more than 1,000,000 emails a month, one or more sender domains can be allocated to a dedicated IP address, which also lets a company separate the traffic of different applications, parent companies or subsidiaries. A suppression list stops resends to recipients who cannot be reached.

Tracking and reporting

Status information comes back by API callback (webhook) or as a non-delivery report. It covers delivery status, the reason a message could not be delivered, emails blocked because the recipient is on the suppression list, and open and click rates. For each final SMTP status the page lists details such as the recipient MTA, the timestamp, the operating system and the email client. Status data can feed business processes and applications automatically, which the page connects to list hygiene, bounce and traffic management and a better domain reputation.

Live search finds outbound emails by time period, message ID, sender or recipient, with detailed status for the past 45 days. Trend views show developments in delivery, soft and hard bounces and dropped messages so that a team can act on them.

Administration runs through the Enterprise Administration Service portal, myEAS, with real-time dashboards, live tracking of transmission jobs and a self-service area where IT admins manage their Transactional Email configuration. The GraphQL Reporting API returns usage detail records and event data automatically, and as an option Retarus delivers the data behind its dashboards in the Prometheus data model to the customer's own monitoring system. Developers also get a Retarus Docs MCP Server, which gives AI tools read-only access to the public documentation and, the FAQ stresses, no access to customer data, credentials or production systems.

Add-ons

Three add-ons extend the core service. Trace and Recover lets staff in a service or contact center find and resend lost transactional emails without access to the business application that sent them. Message Signing digitally signs emails sent from an SAP system, for confidentiality, integrity and authenticity. AntiVirus MultiScan checks outgoing messages with the scanners of Retarus Email Security, deletes an infected email and reports the details immediately.

Data centers, compliance and integrations

The page lists data centers in the United States, in Europe and in the APAC region, described as self-operated, self-sufficient and redundant, with "No hyperscalers" and local data processing available. It states that all data centers are operated to requirements including EU GDPR, HIPAA, Sarbanes-Oxley, PCI DSS, CAN-SPAM and TISAX. One customer quote mentions access to the interface "from the Swiss data center". Integration pages cover SAP environments, the Microsoft 365 ecosystem, healthcare systems such as Epic and Cerner (described as "HIPAA-compliant messaging"), and CRM, marketing automation and e-commerce systems.

Pricing, onboarding and support

The site publishes no prices; buyers book a demo or contact sales. Onboarding is handled by Retarus: an experienced team takes care of onboarding and go-live, and devoted service management follows. The support section promises "No call center nor chatbots" and experts who stay involved from scope and migration through production. The FAQ says Retarus draws on "thousands of successful migrations and onboardings". Customer stories include twoday, which uses the service for its Addo Sign digital signature product, Starmind, Solvay and Groupama.

Who it suits

Retarus suits large companies and regulated organizations whose applications send high volumes of business-critical mail: banks, insurers, healthcare providers, companies running SAP, and groups with many subsidiaries that need separate traffic and a single operator. Buyers who want throughput and delivery written into a contract, data processed in self-operated centers, and a named team for migration will find those commitments on the product page. A small team that wants to sign up online and start sending the same afternoon is not the audience the site is written for.