General

The SMTP (Simple Mail Transfer Protocol) service is the core of IceWarp Server's functionality, as it is the protocol used for sending messages from one server to another.

Figure. Mail management: General view.

See also the Antispam Flowchart chapter within the Antispam Reference section.

Spool Manager - Main Features

(the Mail > General > Advanced tab)

  • Independent emails going to the same target domain are sent using one SMTP session.
  • It is possible to set limits for messages sent to one domain per one minute.
  • It is possible to set limits for messages sent from one domain per one minute.
  • There are five queues with different sending speed. The appropriate queue is chosen according to:
  • message priority in the message header
  • whether it is a mailing list/backup domain delivery/distributed domain delivery
  • whether it is a retry attempt

Internal outgoing queues are sorted by Priority (0-4), where 4 is the fastest. Sending speeds are relative - every queue is 2x as fast than a queue with the closest lower priority. Administrator can see current message priority queue in Logs > Message Queue section of the administration console.

Priority flags are respected and standard email is prioritized over:

  • Mailing lists

  • Backup domains

  • Distributed domains

  • Any entries 

Example:

Priority 1 or 2 are emails sent via mailing list or coming from backup domains. If retried they would be showing Priority 0.