Email Activities

One activity, email.send, delivers a message over SMTP. Use it for notifications and alerts at the end of a workflow.

Setup

Every connection setting can come from the activity, from the worker's configuration, or from an environment variable, resolved in that order:

Setting	Input field	Environment variable	Fallback
Host	smtp_host	MOCO_SMTP_HOST	—
Port	smtp_port	MOCO_SMTP_PORT	465 with use_ssl, otherwise 587
Username	username	MOCO_SMTP_USERNAME	—
Password	password_secret_key	MOCO_SMTP_PASSWORD	—

So a deployment with SMTP configured on the worker only needs the message fields: from_address, to_addresses, subject and a body.

password_secret_key is the name of a secret, not the password. Authentication is attempted only when a username and a password both resolve.

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email.send

Sends one message, optionally with an HTML body, CC/BCC recipients and attachments.

Input

Field	Type	Required	Default	Description
from_address	str	yes	—	Sender address
to_addresses	list[str]	yes	—	Primary recipients
subject	str	yes	—	Subject line
body_text	str	no	null	Plain-text body
body_html	str	no	null	HTML body. Set both bodies to send a multipart message
cc_addresses	list[str]	no	null	CC recipients
bcc_addresses	list[str]	no	null	BCC recipients
reply_to	str	no	null	Reply-To address
custom_headers	dict[str, str]	no	null	Extra message headers
attachments	list[EmailAttachment]	no	null	Files to attach
smtp_host	str	no	MOCO_SMTP_HOST	SMTP server host
smtp_port	int	no	see Setup	SMTP server port
username	str	no	MOCO_SMTP_USERNAME	SMTP username
password_secret_key	str	no	MOCO_SMTP_PASSWORD	Secret name holding the SMTP password
use_tls	bool	no	true	STARTTLS on a plain connection
use_ssl	bool	no	false	Implicit TLS from the first byte (usually port 465)
timeout	int	no	30	Socket timeout in seconds, independent of the activity timeout

EmailAttachment

Workers have no shared filesystem with the caller, so attachment content travels inline as base64.

Field	Type	Required	Default	Description
filename	str	yes	—	Name shown to the recipient
data	str	yes	—	Base64-encoded file content
content_type	str	no	"application/octet-stream"	MIME type

Output

Field	Type	Description
success	bool	True when at least one recipient was accepted — see the caution below
message_id	str | null	Message-ID of the sent message
recipients_accepted	list[str]	Addresses the server accepted
recipients_rejected	dict	Addresses the server refused, mapped to the server's reason

Examples

An alert with both bodies, from moco-examples/web-crawler-demo/src/web-crawler-demo.yaml:

- activity:
    type: email.send
    name: send_availability_alert
    retry_policy:
      timeout_sec: 30
    input_data:
      smtp_host: "{{ smtp_host }}"
      smtp_port: "{{ smtp_port }}"
      username: "{{ smtp_username }}"
      password_secret_key: "{{ smtp_password_key }}"
      from_address: "{{ alert_from }}"
      to_addresses: "{{ alert_to }}"
      subject: "NYU tour availability found ({{ len(found_dates) }} date(s))"
      body_text: >-
        Tour availability was found for NYU in-person visits.
      body_html: >-
        <h2>NYU Visit Tour availability found</h2>

Attaching a generated report, relying on the worker's SMTP configuration:

- activity:
    name: mail-report
    type: email.send
    input_data:
      from_address: "reports@example.com"
      to_addresses: ["ops@example.com"]
      subject: "Daily report {{ run_date }}"
      body_text: "The report for {{ run_date }} is attached."
      attachments:
        - filename: "report-{{ run_date }}.csv"
          content_type: "text/csv"
          data: "{{ base64.b64encode(report_csv.encode()).decode() }}"
    output_name: mail_result   # -> success, message_id, recipients_accepted, recipients_rejected

success does not mean every recipient got it

success is true when the server accepted any recipient. If you need all-or-nothing delivery, check that recipients_rejected is empty:

- abort:
    condition: "{{ len(mail_result['recipients_rejected']) > 0 }}"
    type: raise
    message: "Rejected recipients: {{ mail_result['recipients_rejected'] }}"

Retries re-send the message

email.send defaults to 2 attempts and there is no deduplication — a retry after a timeout can deliver the message twice. Set max_attempts: 1 where a duplicate would be worse than a miss.