PChannel vs. Email:
The Question of Custody

Email ecosystem

Note: The following description of the email ecosystem is a broad generalization, applicable to a majority of real-world scenarios. Exceptions do exist. This is not meant to be an authoritative narrative.

In the email ecosystem, messages are stored on servers which communicate with each other using the SMTP protocol. Once you hit “Send,” your message is uploaded to your mail server, then routed automatically to the recipient’s mail server, where it goes into his inbox and awaits a request from its client(s) to download the message to his local device. This download is handled under a different protocol (typically IMAP or POP3). The process is this:

• Sending Outbound Mail: When you hit "send," desktop email clients commonly submit outgoing mail using SMTP. Webmail and some applications use HTTPS or provider-specific interfaces. .
• Server-to-Server Relay: The outgoing server uses DNS to look up the recipient's domain and relays the message via SMTP to the recipient's mail server.
• Message Retrieval: Receiving and downloading emails to your device is handled by different protocols such as IMAP or POP3. SMTP only handles sending and relaying.

PChannel ecosystem

One of our main goals driving the architecture of the SMFX protocol (under which PChannel is constructed) is to avoid using cloud mailboxes as the long-term correspondence archive. So PChannel works like this:

• Sending an outbound Message: When you post a Message in PChannel, the app uses SMFX over HTTPS to submit a separate package for each destination node to the Relay, currently at https://bcr1.pchannel.cc. Three destination nodes mean three separately addressed packages. The Relay routes packages; it does not manage Channel membership.
• Relay to recipient: Each recipient’s app checks the Relay for packages addressed to it and retrieves those available. Unacknowledged packages expire no later than 48 hours after Relay acceptance from the sender; expiration cleanup removes their stored payloads. A recipient who is offline may therefore miss that delivery.
• Recipient custody confirmation: The receiving app validates and stores the Message locally, then acknowledges custody to the Relay. (Note that this confirms receipt by the application—not human reading, approval, or business acceptance).
• Removal of the temporary Relay copy: After accepting the destination node’s acknowledgment, the Relay deletes that package’s payload from its active storage, independently of other recipients’ deliveries. (Limited custody metadata remains). Participants retain their local correspondence; backups, archives, and exports may contain additional copies.

* Here, “durable copies” means the continuing correspondence archive. Temporary Relay storage and hosting backups are separate considerations.

Current alpha limitation: Message content is not yet end-to-end encrypted or cryptographically concealed from the Relay.

The Verdict: PChannel makes correspondence easier to manage

Email:

Mail servers commonly store all of your messages until you deliberately archive them locally and delete them from the server. Until both sender and receiver do this, copies remain “in the cloud.”

• Your company’s settings and deletion practices govern its copies.
• Each recipient’s settings and practices govern theirs.
• Deleting your copy does not delete anyone else’s.

Copies may therefore remain “in the cloud” until every party’s server-held copies have been removed (subject also to backup and retention policies of others).

CAVEAT : If both sender and receiver own and maintain their own mailservers, then durable copies of messages will be retained “in-house” at each end. PChannel provides local correspondence records without requiring each participant to operate a mail server.

PChannel:

PChannel makes removal of temporary Relay payloads part of the normal delivery lifecycle. Participants do not need to coordinate server-mailbox deletion across companies to achieve that result. The continuing correspondence record resides on participants’ computers, while their backups, archives, and exports remain under their respective control.

PChannel’s architecture reduces the the administrator’s doubt about “where is my information, and who has access to it?” The point is not that it is inherently more secure—we address that topic elsewhere. The point of this discussion is that you know where your information was-and-was-not delivered to (bad grammar, but clear meaning).

As in any case of data custody, control depends on a trust-relationship of all custodial parties.

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