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Message Filtering

Message Filtering

WildDuck has a built-in message filtering system. This is conceptually similar to Sieve, but filters are not scripts — they are structured rules managed via the API.

How Filters Work​

When a message is received (via Haraka inbound SMTP), WildDuck evaluates all applicable filters in order. Each filter consists of a query (conditions to match) and an action (what to do with matching messages).

Filters are evaluated for every incoming message. Multiple filters can match the same message, and their actions are applied in sequence.

Filter Conditions​

Filters can match on message properties:

  • From — sender email address
  • To — recipient email address
  • Subject — message subject line
  • Size — message size (greater than / less than)
  • List-ID — mailing list identifier header
  • Text — full-text content match

Conditions support exact match, contains, starts with, and other comparison operators.

Filter Actions​

When a filter matches, one or more actions can be taken:

ActionDescription
Move to mailboxDeliver to a specific mailbox instead of INBOX
ForwardForward the message to another email address or HTTP URL
Mark as seenSet the \Seen flag on delivery
Mark as flaggedSet the \Flagged flag on delivery
Mark as spamRoute message to Junk folder
DiscardSilently discard the message
AutoreplySend an automatic reply to the sender

Forwarding​

Messages can be forwarded to:

  • Email addresses — the message is re-sent to the specified address
  • HTTP URLs — the message is POSTed to a webhook endpoint (useful for integrations)

Forwarding includes loop detection to prevent infinite forwarding chains. Forward rate limits apply (default: 2000 forwards per day per user).

Managing Filters via API​

Filters are managed through the WildDuck HTTP API:

  • GET /users/:user/filters — List all filters for a user
  • POST /users/:user/filters — Create a new filter
  • GET /users/:user/filters/:filter — Get filter details
  • PUT /users/:user/filters/:filter — Update a filter
  • DELETE /users/:user/filters/:filter — Delete a filter

Autoreplies​

WildDuck has a dedicated autoreply (vacation message) system:

  • GET /users/:user/autoreply — Get autoreply status
  • PUT /users/:user/autoreply — Set autoreply with text/HTML content

Autoreplies support:

  • Date ranges — start and end dates for the vacation period
  • Custom subjects — override the default reply subject
  • Text and HTML — both plain text and HTML body
  • Frequency limiting — by default, only one autoreply per sender every 4 hours to prevent reply storms