Transactional EmailTechnical Specifications
Made for throughput. With Retarus Transactional Email you can be sure your emails are reaching their recipients. All thanks to a state-of-the-art email infrastructure, a contractually specified processing throughput of up to several million emails per hour, high inbox placement rates, and optimal sender reputation.

Retarus Transactional Email
API for sending emails
from applications
REST v2SMTP
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- Guaranteed processing capacity of up to 10 million emails per hour
- Permanently high, guaranteed throughput rate
- High availability and disaster recovery plan
- Global availability and local processing
- Detailed status notifications
- Above-average inbox placement rate
- Differentiation of transactional, marketing, and P2P emails possible
- No internal email infrastructure needed
- Connection via REST API or SMTP adapter
- Authentication via Auth Basic or source IP
- Encryption based on sender domain via enforced TLS
- Ensuring the authenticity and integrity of the sending system using DNSSEC
- Check performed by Retarus AntiVirus MultiScan
- Password-protected attachments possible
- Optional CNAME function reduces the probability that an email is classified as spam
- Calculation of opening rates with open tracking and link tracking
- FreeMarker templating support
- Easy processing of multi-recipient jobs with up to 1,000 recipients at the same time
- Integrated campaign support
- Multi-level service level agreements (SLA
s ) available - 24/7 support in multiple languages
- Support for international compliance requirements such as the EU GDPR, HIPAA, Sarbanes-Oxley, PCI DSS or CAN-SPAM
- Continuous development
CSA certification

Retarus data centers are CSA certified. The Certified Senders Alliance (CSA) aims to increase the quality of commercial emails (for example, newsletters, invoices, and order confirmations). This is done by creating quality standards that must be technologically and legally observed.
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- No spam score check for CSA-certified ISPs and technology partners; high rate of delivery to the recipient’s inbox
- Higher throughput per unit of time, no or reduced throttling
- Unsubscribe options
- DKIM signature for secure authentication
- Protection against fake sender addresses via SPF
- Effective early warning system thanks to CSA mechanisms
- Emails sent in compliance with current privacy regulations
- Large international ISP network
Reputation management
SPFDKIMDMARC
Outgoing emails are checked to determine the reputation of the sender. The authorization of senders is evaluated by implementing the following verification functions: SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail) and DMARC (Domain-based Message Authentication, Reporting and Conformance). Classified emails that do not pass validation are isolated in a quarantine.
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- Reputation management – SPF, DKIM and DMARC validation
- Assignment of dedicated IP addresses (recommended when sending more than 1,000,000 emails per month)
- Dynamic IP routing according to sender domain
- Support of IPv4 and IPv6
- Ability to send large emails (attachment limiter) up to 20 MB
- Filter function for critical file types (e. g. exe) and role-based recipient addresses (e. g. noreply@)
- Less blacklisting thanks to different IP addresses for transactional, marketing, and P2P emails
- Blacklist and reputation monitoring with monitoring of more than 50 international blacklisting providers
- Blocking of unknown recipient addresses (suppression list)
- Feedback loop service automatically reports if and which emails are rejected by recipients and prevents resending to recipients who have declined receipt of specific emails from the ISP
- SNDS (Smart Network Data Services) reporting supplies data that can be used to evaluate the reputation of Microsoft communication partners and optimize as needed
- Spam Score Check scans emails before they are sent to determine their spam probability, based on known factors such as formatting, hyperlinks, and so on
- Smart Delivery Optimization intelligently manages the batch sending of emails per sending domain and can therefore automatically adapt the sending behavior to the requirements of each ISP and email provider. This actively minimizes the risk of being blocked or even blacklisted.
Global availability
Local processing
Compliance
GDPRHIPAAPCI-DSSCAN-SPAM
Retarus Transactional Email is available worldwide as part of the Retarus Enterprise Cloud. Retarus can guarantee local data processing upon request. All data centers are operated according to the latest standards and fulfill strict requirements set forth by financial service providers and the health care industry.
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- Failover or load-balancing options in Retarus’ data centers with local, independent access in Europe, Asia, and the US
- Integration via modern API
s or SMTP - Multi-client capability thanks to multi-domain configuration
- Support for international compliance requirements such as the EU GDPR, HIPAA, Sarbanes-Oxley, or PCI DSS, CAN-SPAM
Address rewriting (outbound)
The rewriting of sender addresses for outgoing emails simplifies, in many cases, the implementation of company-internal policies. For example, when company-internal domains should not be used for external communication. Therefore, Retarus offers the option of automatically rewriting your envelope from-address for outbound emails so that any replies can be rerouted directly to a dedicated inbox.
Secure Document Handling
Secure Document Handling allows you to encrypt the files you want to attach to your outgoing emails. The files are automatically added to a ZIP archive in the Retarus infrastructure and encrypted with a password. Retarus sends the passwords separately to the recipients of the corresponding emails. To ensure the best possible protection for your recipients, this service is offered together with our AntiVirus MultiScan service.
Comprehensive
status messages
Detailed monitoring, which Retarus Transactional Email makes available in real time, can be used to check the status of a sent email at all times.
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- Status information via API callback (webhook) or non-delivery report (NDR)
- Information about the delivery status, reason for undeliverability, blocked emails sent to recipients recorded in the suppression list, or open and click rates, etc.
- Detailed information about each final SMTP status, e.g. recipient MTA, time stamp, operating system, email client, etc.
- Automated integration of status information in business processes and applications
- Simple master data maintenance (list hygiene), easier bounce and traffic management, better domain reputation
- Live monitoring in the EAS Portal for tracking transmission jobs in real time
- Live search makes it possible to search through transmission jobs in real time
Response Management
Bounce and Response Manager
InboundOutbound
The key add-on to Transactional Email for inbound emails. The Bounce and Response Manager provides you and your employees an overview of your inbox at all times, even when email volumes are high. Keep out of office replies and hard bounces separate from legitimate customer inquiries to facilitate faster response and reply times.
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- Manage, organize, and route incoming emails, especially responses to transactional emails
- Traffic handling and workflow automation for marketing, support, and contact center
- Meets the highest performance and compliance requirements especially for complex corporate environments
- Completely cloud based; integral component of the Retarus Secure Email Platform
- Automated virus scan for all incoming emails
Functional overview of Retarus Transactional Email
Email delivery | REST v2 | SMTP |
---|---|---|
Multi-recipient jobs | ||
Guaranteed throughput | ||
Smart delivery optimization | ||
Invoicing according to account/cost center | ||
Open tracking and link tracking | Coming soon | |
AntiVirus MultiScan | ||
Secure Document Handling | Coming soon | |
Campaign support | ||
User-defined X header | ||
Unsubscribe support | Coming soon | |
Envelope sender address rewriting | ||
Enforced TLS | ||
Templating Management | ||
Reference information |
Service options | REST v2 | SMTP |
---|---|---|
IP whitelisting (API) | ||
Authentication via sender IP | ||
Multi-client capable (multi-domain configuration) | ||
Data format | JSON | SMTP/MIME |
Global processing | EU CH USA APAC |
EU CH USA APAC |
Reporting | REST v2 | SMTP |
---|---|---|
Status information for each email | API callback (webhooks) | API callback (webhooks) |
Tracking via live monitoring (EAS) | Search via live search (EAS) | Detailed delivery reporting (EAS) | SNDS reporting |
Reputation management | REST v2 | SMTP |
---|---|---|
Dedicated IP (optional) | ||
Blacklist monitoring | ||
SPF / DKIM / DMARC | ||
Support of IPv4 and IPv6 | ||
Suppression list (hard bounces) | ||
Feedback loop service | Email API callback | Email API callback |
Registered sender domain | ||
CSA certified |