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 in _id order (normally creation order). Multiple filters can match the same message. For actions that take a single value, the first matching filter that sets that action wins. Labels and forwarding targets from matching filters are combined. Domain allow/block rules are considered before user filters, and the spam-level policy is applied after them. A filter that explicitly chooses a destination mailbox takes precedence over routing to Junk.

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
• Has attachment — whether the message has attachments

Conditions support substring matching and regular expressions.

For the related account labels exposed by WildDuck, see Labels.

Filter Actions

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

Action	Description
Move to mailbox	Deliver to a specific mailbox instead of INBOX
Forward	Forward the message to another email address or HTTP URL
Mark as seen	Set the \Seen flag on delivery
Flag	Set the \Flagged flag on delivery
Spam	Route message to Junk Mail folder
Delete	Do not store the matching message
Labels	Apply named labels to matching messages

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