Template:Email agents/Metadata

Note: In discussing machine-level models of email systems, the words 'actor' and 'agent' mean computer processes. In discussing administrative functions, these words have their original plain-English meanings - an individual or organization. The usage of these words should be clearly stated in any context where it is not obvious. In this article, we are using the plain-English meanings.

Actors and their roles in an email system

Actors include Users and Agents
Agents may play more than one role
Typical roles include Transmitting, Receiving, Forwarding, and Delivery.

Roles defined by their responsibilities

Author
- Originate messages
- Provide a password or other means of authentication

MSA - Mail Submission Agent
- Authenticate the Author
- Manage Author accounts

Transmitter
- Spam Prevention
  - rate limits, content analysis, alerts
  - respond to spam reports
  - maintain reputation
- Authentication
  - RFC compliance
  - IP authorization (SPF, SID, CSV, ...)
  - signatures & key management (DKIM ...)
  - Return Address validation code
- Process SMTP Rejects

Receiver
- Block DoS
- Authenticate Sender
  - HELO, Return Address, Headers, Signature
  - reject forgeries
- Assess reputation
  - whitelists
- Filter spam
- Add authentication headers
- Manage Recipient accounts/options
  - whitelisting, blacklisting, filtering, blocking, forwarding
- Process spam reports, DSNs

Forwarder
- Authenticate upstream Agent
- Set up forwarding to downstream Agent
  - check RFC compliance
  - set up authentication records
  - submit forwarding request, wait for approval
- Manage Recipient accounts
  - maintain database of forwarding addresses
  - suspend account when a message is rejected
  - communicate w Recipient re  "      "
- Maintain reputation as a trusted Forwarder
  - certifications
- Process SMTP Rejects

MDA - Mail Delivery Agent
- Authenticate upstream Agent
- Sort and store messages
- Provide access for Recipients
  - POP3, IMAP, Webmail
- Manage Recipient accounts/options
- Relay spam reports to Receiver (or don't accept them)

Recipient
- Set up accounts with each Agent
- Select options in each account
- Report spam to Receiver

Mediator
- Receive - Process - Resend automatically
- Acts as an Agent, but
- Classified as a User for simplicity