specs/044-mail-send.md

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# Spec: Mail Send Action

## Status

Partially implemented.

Conformance covers one local delivery and configuration errors. SMTP
authentication, MIME encoding, HTML conversion, and attachments belong in mailer
unit and integration tests.

## Scope

This spec defines the `mail.send` action boundary. It does not define SMTP
protocol internals or message encoding.

## Goal

Workflow authors can send a notification using the DAG's SMTP configuration.

## Behavior

`mail.send` uses the DAG-level `smtp` configuration. The action accepts sender,
recipient, subject, and message fields under `with`. Successful execution delivers
a message with the configured subject and recipient.

With `with.mailbox`, `mail.send` sends through that mail account instead, as
[Spec 073](073-mailbox-actions.md) defines.

## Errors

An empty recipient fails before connecting to SMTP. An attachment that does not
exist or cannot be read fails the step before connecting, with an error naming
the attachment. An empty attachment file is attached as an empty file. SMTP OAuth configuration
requires a username and cannot be combined with a password; invalid combinations
fail `dagu validate` with a diagnostic identifying the conflict.

## Examples

```yaml
smtp:
  host: localhost
  port: 2525
steps:
  - action: mail.send
    with:
      from: sender@example.com
      to: recipient@example.com
      subject: Test Subject
      message: hello world
```