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Comparison · Comms
Mailu vs Slack
A side-by-side editorial comparison of Mailu and Slack — release velocity, themes, recent moves, and the top alternatives to consider.
Mailu vs Slack: at a glance
What is Mailu?
A mail server whose entire visible output is patching other people's code.
Mailu is a self-hosted mail suite shipped as a Docker compose stack, and the 2024.06.x branch shown here is its maintenance line. Every release in the window is a single-issue patch — a Roundcube bump, a CVE fix, an autoconfig tweak. The cadence looks high at ten pinned releases in five months, but each carries one change.
What is Slack?
Slack's app platform is being rebuilt around agents, with the SDKs clearing old ground behind it.
Slack's developer changelog currently runs on two tracks. One is agent infrastructure: agent apps now receive context about whatever channel, DM, thread, canvas, or list the user has open when they message the app, and a new manifest-declared messaging experience defines how agents converse. The other is SDK maintenance at a steady clip — Bolt for JS v5, a batch of Node Slack SDK majors, and three CLI releases inside a month.
Mailu vs Slack: editorial side-by-side
Mailu
5.0COMMS
A mail server whose entire visible output is patching other people's code.
◆ Current state
Mailu is a self-hosted mail suite shipped as a Docker compose stack, and the 2024.06.x branch shown here is its maintenance line. Every release in the window is a single-issue patch — a Roundcube bump, a CVE fix, an autoconfig tweak. The cadence looks high at ten pinned releases in five months, but each carries one change.
◆ Where it's heading
Most of what Mailu ships is downstream maintenance of its bundled components, Roundcube above all, which drove three of these ten releases. The project's own work here is defensive: escaping user-controlled fields in generated sieve scripts, setting X-Forwarded-By, adapting to Microsoft's new autodiscover. This is a product in steady-state operation, where the release notes track what upstream broke rather than what Mailu decided to build.
◆ Prediction
The next pinned release will most likely be another Roundcube or Alpine bump, since component upgrades triggered half the releases here. These entries say nothing about what is happening on the main branch.
Slack
6.3COMMSCOLLAB
Slack's app platform is being rebuilt around agents, with the SDKs clearing old ground behind it.
◆ Current state
Slack's developer changelog currently runs on two tracks. One is agent infrastructure: agent apps now receive context about whatever channel, DM, thread, canvas, or list the user has open when they message the app, and a new manifest-declared messaging experience defines how agents converse. The other is SDK maintenance at a steady clip — Bolt for JS v5, a batch of Node Slack SDK majors, and three CLI releases inside a month.
◆ Where it's heading
The expansion is happening on the agent side while the SDK work removes rather than adds: axios swapped for native Fetch, Workflow Steps from Apps deleted, Node 20 set as the floor. Alongside that, a new Block Kit container block and the switch to pulling desktop notification text from blocks first both push more of the app experience into structured, app-rendered surfaces. Read together, Slack is moving the platform's center of gravity from configured workflow automation toward apps that hold a conversation with context.
◆ Prediction
Expect the next platform releases to widen what agents can receive and render — more context surfaces passed automatically and more Block Kit primitives to display results — while the CLI and SDKs keep their current maintenance cadence.
Alternatives to Mailu and Slack
Other Comms products tracked by Sparkpulse, ranked by recent ship velocity. Each card links to a full editorial trajectory and lets you pivot into a head-to-head comparison with either Mailu or Slack.
Chatwoot
Chatwoot added voice, then pointed its AI agent at the tickets it already resolved.
Roundcube
After four years, Roundcube 1.7 lands — and the release stream is otherwise all CVEs
Signal Desktop
Signal's beta train is quietly handing group admins real moderation powers.
Notion
Notion is turning itself into the place other companies' agents come to work.
Bird
Monthly digests showing AI chat latency cut hard, in a feed that repeats itself
Recent activity from Mailu and Slack
Latest ship moves from both products, interleaved chronologically. ⚡ = editorial spark.
- 1d agoSlackRelease: Slack CLI v4.6.0
- 5d agoMailuAutoconfig fix for modern K-9 Mail
- 7d agoMailuRoundcube 1.6.17 closes two CVEs
- 10d agoSlackRelease: Slack CLI v4.5.0
- 12d agoMailuSets X-Forwarded-By in response to a GHSA advisory
- 16d agoSlackRelease: Bolt for JS v5
- 17d agoSlackRelease: Multiple Node Slack SDK package updates
- 18d agoSlackDesktop notifications now pull text from blocks first
- 26d agoMailuAdmin UI keeps form values on failed submit
- 29d agoSlackAgent context has landed ⚡
- 1mo agoMailuEscapes sieve fields, fixing autoreplies with special characters
- 2mo agoMailuRoundcube 1.6.16 and carddav 5.1.3 close CVE-2026-49217
Frequently asked questions
What is the difference between Mailu and Slack?
They serve adjacent needs but don't currently overlap on shipped themes. Slack is currently shipping more aggressively (velocity 6.3 vs 5.0), with 1 editorial sparks in the last 30 days against 0. See the at-a-glance table above for a side-by-side breakdown of velocity, recent sparks, and editorial themes.
Is Mailu better than Slack?
Sparkpulse doesn't pick a winner — we score release velocity, not feature parity. Slack is currently shipping more aggressively (velocity 6.3 vs 5.0), with 1 editorial sparks in the last 30 days against 0. For your specific use case, the alternatives sections above list other Comms products to evaluate alongside.
What are the best alternatives to Mailu?
Top Mailu alternatives in Comms are ranked by recent ship velocity. Browse the "Mailu alternatives" section above for the current picks, or visit /alternatives/mailu for the full list with editorial commentary on each.
What are the best alternatives to Slack?
Top Slack alternatives in Comms are ranked by recent ship velocity. Browse the "Slack alternatives" section above for the current picks, or visit /alternatives/slack for the full list with editorial commentary on each.