Mattermost Notification Filters: Unresolved Deduplication Across Channels

Answer

No. Mattermost does not provide a native system-level rule to collapse or deduplicate identical alerts that are posted to different channels. Notification delivery is evaluated per user per channel per post, and the server treats each channel post as an independent notification event. There is no built-in global deduplication policy, and no confirmed native feature for cross-channel deduplication is available in the core product today.

What is confirmed

• Per-channel notification preferences can override global settings. Users and admins can set mentions, keywords and desktop/mobile push per channel.
• Do Not Disturb is global and cannot be scoped to individual channels via the standard UI.
• The Notification Filters plugin can silence alerts containing specific keywords. It operates on post content within a channel and has no stateful awareness of duplicate payloads arriving in different channel IDs.
• Notification logic is processed at the user-per-channel level. Each post triggers its own notification path.

Likely explanation for the unresolved behavior

Because the notification engine has no cross-channel correlation, identical alert text posted to Channel A and Channel B will generate two separate notifications for the same user. The Notification Filters plugin cannot identify duplicates across channels because it lacks a shared deduplication store and event identity. Global policies such as Do Not Disturb apply to all channels, so channel-specific silence windows are not possible without external control.

Practical steps for this case

1. Avoid posting the same event to multiple channels from the source. Route each alert to a single canonical channel and use Mattermost mentions or channel membership to reach the right teams.
2. If multi-channel posting is required, add keyword-based silencing with Notification Filters on the secondary channels for the noisy alert patterns you can identify.
3. For true deduplication, handle it before Mattermost. Use a webhook middleware or integration layer that tracks an event identifier and suppresses subsequent posts to other channels within a short window. This preserves per-channel overrides because the post is never created in the suppressed channel.

Permission boundaries: there is no permission or admin setting for a global deduplication policy because the feature does not exist. Admins can manage Notification Filters plugin configuration and global notification defaults, but deduplication would require custom integration owned by the integration owner, not Mattermost system permissions.

One diagnostic detail that changes the recommendation: are the duplicate alerts generated by the same source system posting the same event ID to multiple channels, or by different sources that happen to produce identical text? If a stable event ID is available, middleware deduplication is feasible. If not, only channel routing or keyword silencing is practical.