mesh-catalog/modules/mesh-mail/README.md

mesh-mail — the operator's mail accounts, watched and said on the bus

One module holds the operator's mail accounts, watches them, and says each change of a message on the bus for the modules the operator grants it to (novox/hq ADR 0359, research 049 document 02). One instance, on the control-node. This is the first stage: accounts of the kind imap, read-only. Nothing here flags, moves, deletes, drafts or sends.

What it does

• Watches. For each account it keeps one connection: IDLE on the inbox, ended and begun again every two minutes (which proves the server still answers), and a look at every other folder every five minutes. Folders are opened read-only and bodies are peeked, so watching never marks a message seen.
• Indexes. One row per message and folder in its own database (postgres-database): metadata, flags, the text for search, and the attachments' references. Each attachment is kept once, by its SHA-256, in its bucket (s3-bucket, from minio).
• Says each change. A message added, its flags changed, or removed is said as the event mail.<account>.message.<added|changed|removed>: account, folder, uid, message id, date, sender, recipients, subject, size, flags and attachment references; never the body, never an attachment's bytes. The events go to the module's own stream MAIL, kept seven days, never to the shared EVENTS stream (novox/hq ADR 0363); a module hears an account's part only when its consumes names mesh-mail and the setting grants names it for that account. The first look at a folder indexes what is there and says nothing: the bus hears what changed since the watch began. The keeper writes each event in the same step as the change it says; the bundle says it through the runtime and removes it once the bus took it.

Its settings, both trusted

accounts — per account name (a lower-case token, which names the account on the bus and its secret):

{"mesh": {"kind": "imap", "address": "<the address>",
          "incoming": {"host": "<the IMAP server>", "port": 993, "security": "tls"},
          "outgoing": {"host": "<the SMTP server>", "port": 465, "security": "tls"},
          "folders": ["optional: the folders watched besides the inbox; every folder when left out"]}}

outgoing is read and never used in this stage. A second imap account on another server is one more entry and one more password; no code changes. user signs in under another name than the address.

grants — per account, who may read its mail: a module's name (on every machine), <machine>.<module>, or person.<name>. Nobody by default. It restricts the stream MAIL on the bus (a person's entry grants nothing there) and the tools mail_search and mail_read.

The password of an account is the own secret mail-credential-<account>, given at the desk; the mesh never makes one.

Its tools

Tool	Answers
mail_accounts	each account's kind, state and why, when its server last answered, its folders; the address only to a caller granted it
mail_search	messages of the accounts the caller is granted, by every word of a query, newest first, no body
mail_read	one message's metadata and text, or one attachment's bytes, to a caller granted its account
mail_health	healthy; unhealthy naming the account and why (connection down, or no answer for five minutes); waits naming mail-credential-<account> while its password is not given

The caller is the runtime's word, never an argument.

Its processes

prepare brings the index's schema to this version's (numbered migrations, and schema.sql for a fresh database). keep watches the accounts and is judged by its unit. watch judges every minute and is judged by mail_health.