Inbound delivery

Inbound Internet mail reaches the JKMail SMTP service, passes policy and spam checks, and is then delivered to the appropriate hosted mailbox when accepted.

Outbound delivery

Outbound mail is queued and delivered according to Postfix routing and the destination domain's DNS.

SMTP status classes

• 2xx: the SMTP operation was accepted.
• 4xx: temporary failure; delivery may be retried.
• 5xx: permanent failure for that attempt or recipient.

Queue behaviour

A deferred message remains queued for retry according to the mail-server policy. Do not assume a temporary 4xx response means the message has been permanently lost.