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Email Delivery Pipeline

Trace one message from client submission through MX lookup, SMTP retry, filtering, and final mailbox delivery.

MUAOutboundDNS MXInbound MXFilterMailboxmailSubmission boundary: user to provider
Sender
AUTH + submit
Outbound queue
awaiting handoff
DNS
idle
Inbound MX
not contacted
Filter
idle
Mailbox
empty
Step 1 / 7The mail client submits the message to its provider

The laptop is not delivering mail to Berlin directly. It authenticates to its own submission server, usually on port 587, and hands the message off there first.

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