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Version: 0.1

Status: Stable

Authors: Adam Babik [email protected], Oskar Thorén [email protected], Samuel Hawksby-Robinson [email protected] (alphabetical order)


Being mostly offline is an intrinsic property of mobile clients. They need to save network transfer and battery consumption to avoid spending too much money or constant charging. Waku protocol, on the other hand, is an online protocol. Messages are available in the Waku network only for short period of time calculate in seconds.

Waku Mailserver is a specification that allows messages to be stored permanently and to allows the stored messages to be delivered to requesting client nodes, regardless if the messages are not available in the network due to the message TTL expiring.


From the network perspective, a Mailserver is just like any other Waku node. The only difference is that a Mailserver has the capability of archiving messages and delivering them to its peers on-demand.

It is important to notice that a Mailserver will only handle requests from its direct peers and exchanged packets between a Mailserver and a peer are p2p messages.

Archiving messages

A node which wants to provide Mailserver functionality MUST store envelopes from incoming message packets (Waku packet-code 0x01). The envelopes can be stored in any format, however they MUST be serialized and deserialized to the Waku envelope format.

A Mailserver SHOULD store envelopes for all topics to be generally useful for any peer, however for specific use cases it MAY store envelopes for a subset of topics.

Requesting messages

In order to request historic messages, a node MUST send a packet P2P Request (0x7e) to a peer providing Mailserver functionality. This packet requires one argument which MUST be a Waku envelope.

In the Waku envelope’s payload section, there MUST be RLP-encoded information about the details of the request:

[ Lower, Upper, Bloom, Limit, Cursor ]

Lower: 4-byte wide unsigned integer (UNIX time in seconds; oldest requested envelope’s creation time)
Upper: 4-byte wide unsigned integer (UNIX time in seconds; newest requested envelope’s creation time)
Bloom: 64-byte wide array of Waku topics encoded in a bloom filter to filter envelopes
Limit: 4-byte wide unsigned integer limiting the number of returned envelopes
Cursor: an array of a cursor returned from the previous request (optional)

The Cursor field SHOULD be filled in if a number of envelopes between Lower and Upper is greater than Limit so that the requester can send another request using the obtained Cursor value. What exactly is in the Cursor is up to the implementation. The requester SHOULD NOT use a Cursor obtained from one Mailserver in a request to another Mailserver because the format or the result MAY be different.

The envelope MUST be encrypted with a symmetric key agreed between the requester and the Mailserver.

Receiving historic messages

Historic messages MUST be sent to a peer as a packet with a P2P Message code (0x7f) followed by an array of Waku envelopes.

In order to receive historic messages from a Mailserver, a node MUST trust the selected Mailserver, that is allowed to send packets with the P2P Message code. By default, the node discards such packets.

Received envelopes MUST be passed through the Waku envelope pipelines so that they are picked up by registered filters and passed to subscribers.

For a requester, to know that all messages have been sent by a Mailserver, it SHOULD handle P2P Request Complete code (0x7d). This code is followed by the following parameters:

[ RequestID, LastEnvelopeHash, Cursor ]
  • RequestID: 32-byte wide array with a Keccak-256 hash of the envelope containing the original request
  • LastEnvelopeHash: 32-byte wide array with a Keccak-256 hash of the last sent envelope for the request
  • Cursor: an array of a cursor returned from the previous request (optional)

If Cursor is not empty, it means that not all messages were sent due to the set Limit in the request. One or more consecutive requests MAY be sent with Cursor field filled in order to receive the rest of the messages.

Security considerations


The node encrypts all Waku envelopes. A Mailserver node can not inspect their contents.

Altruistic and centralized operator risk

In order to be useful, a Mailserver SHOULD be online most of time. That means users either have to be a bit tech-savvy to run their own node, or rely on someone else to run it for them.

Currently, one of Status’s legal entities provides Mailservers in an altruistic manner, but this is suboptimal from a decentralization, continuance and risk point of view. Coming up with a better system for this is ongoing research.

A Status client SHOULD allow the Mailserver selection to be customizable.

Privacy concerns

In order to use a Mailserver, a given node needs to connect to it directly, i.e. add the Mailserver as its peer and mark it as trusted. This means that the Mailserver is able to send direct p2p messages to the node instead of broadcasting them. Effectively, it will have access to the bloom filter of topics that the user is interested in, when it is online as well as many metadata like IP address.


Since a Mailserver is delivering expired envelopes and has a direct TCP connection with the recipient, the recipient is vulnerable to DoS attacks from a malicious Mailserver node.


Version 0.1

Released May 22, 2020

  • Created document
  • Forked from 4-whisper-mailserver
  • Change to keep Mailserver term consistent
  • Replaced Whisper references with Waku