Develop a detailed technical specification for the construction of transactional SMTP server infrastructure.

Hello!
It is necessary to create a detailed technical + product specification for building the internal infrastructure of transactional SMTP servers for email distributions (messages, confirmations, receipts, promotional and marketing distributions, etc.).

Requirements for the candidate:

1. Experience in developing and implementing mail systems (SMTP servers).
2. Knowledge of email delivery technologies, domain protection (DKIM, SPF, DMARC).
3. Experience with high-load, scalable systems.
4. Knowledge of security and data protection issues.

Format of work execution:

A document in Word or PDF format with a detailed description and architecture diagrams, mockups.

Main tasks:

1. Defining the architecture of SMTP servers:
2. The number of servers participating in the distribution - 6.
3. Recommendations for choosing technologies and protocols for sending emails.
4. Detailed description of server roles: main server, additional servers for load balancing, feedback processing servers (bounce and feedback loops).
5. Mechanisms for routing emails between servers and external mail systems (ISPs).
   
   

Requirements for reliability and scalability:

1. Description of load balancing methods between SMTP servers.
2. Server redundancy (failover and redundancy).
3. Scaling the infrastructure as the volume of distributions increases.
4. Possibility of vertical and horizontal scaling of servers.
   
   

Security:

1. Recommendations for encryption (TLS) for SMTP connections.
2. Configuration of DKIM, SPF, and DMARC records for domain protection.
3. Mechanisms for authenticating users sending transactional emails.
4. Protection against service abuse (e.g., limiting the number of emails, preventing spam).
5. Logs and monitoring of security incidents.
   
   

Email delivery management:

1. Recommendations for preventing emails from going to spam (maintaining a good reputation of IP addresses, checking email content against "spam filters").
2. Detailed description of delivery error handling (bounce) and configuring feedback from mail providers (Feedback Loops).
3. Managing the reputation of IPs and domains used for distribution.
   
   

Performance requirements:

1. Expected volumes of distributions and performance requirements for servers.
2. Latency between sending and delivering emails.
3. Description of limits on the number of emails sent simultaneously.
   
   

Monitoring and logging:

1. Requirements for monitoring systems for server status (load, latency, delivery errors, etc.).
2. Logging of transactions, errors, and successful email deliveries.
3. Mechanisms for alerting about failures and performance drops.
   
   

Interfaces for integration:

1. Possibility of integrating SMTP servers with internal systems (CMS, CRM, etc.).
2. REST API or other mechanisms for transmitting transaction data.
   
   

Data security requirements:

1. Compliance with GDPR and other local data protection regulations.
2. Encryption of personal data during transmission and storage.
   
   

Technical requirements for hardware and software:

1. Recommendations for hardware selection (servers).
2. Description of software (OS, mail software, databases).
3. Requirements for using cloud services (if needed).
   
   

Documentation:

1. Requirements for the final technical documentation regarding the implementation of the infrastructure.
2. Recommendations for training technical specialists to work with this infrastructure.

Expected result:

The output should be a completed document (specification) that details all the aforementioned aspects, including specific technical solutions, recommendations for hardware and software selection, as well as a description of all processes necessary for implementing the SMTP server infrastructure for transactional distributions.