Rspamd
Rspamd 4.3 fixes SPF evaluation order and rejects weak DKIM keys, with results that change.
Comparison · Comms
Stalwart vs Slack
A side-by-side editorial comparison of Stalwart and Slack — release velocity, themes, recent moves, and the top alternatives to consider.
Stalwart vs Slack: at a glance
What is Stalwart?
Stalwart's weekly releases have turned from new standards to correctness fixes.
Stalwart's releases since v0.16.20 are dominated by long Fixed lists across IMAP, JMAP, MTA, DMARC and iTIP. Additions have been small: a PowerDNS provider in 0.16.24, sd_notify and JMAP mailbox behavior in 0.16.26. The most consequential repair is a RocksDB bug in 0.16.26 that rewrote every stored blob on each compaction of the blobs column family, about once per 128MB of new mail.
What is Slack?
Slack now hosts any A2A agent without Slack-specific code.
Slack's developer channel is almost all agent plumbing. On 10 November Slack became an A2A (Agent2Agent) client: a team hosts its own agent, publishes an Agent Card, and Slack calls it when people talk to it, with no request URL, event handling or Slack-specific logic. This follows Slackbot skills managed through Web API methods, a Slack CLI that points coding agents to the Slack MCP server, and a new requirement that Work Objects embeds allow the slack-mcps.com frame ancestor.
Stalwart vs Slack: editorial side-by-side
Stalwart
5.0COMMS
Stalwart's weekly releases have turned from new standards to correctness fixes.
◆ Current state
Stalwart's releases since v0.16.20 are dominated by long Fixed lists across IMAP, JMAP, MTA, DMARC and iTIP. Additions have been small: a PowerDNS provider in 0.16.24, sd_notify and JMAP mailbox behavior in 0.16.26. The most consequential repair is a RocksDB bug in 0.16.26 that rewrote every stored blob on each compaction of the blobs column family, about once per 128MB of new mail.
◆ Where it's heading
After the SCIM v2 release in August, the project has shifted from extending coverage to making existing coverage hold up under real use. The bug reports now describe specific interoperability cases, such as Apple Calendar duplicates and DMARC report formatting, which suggests production traffic is driving the queue. The weekly cadence itself has not changed.
◆ Prediction
Expect more weekly fix releases on the same pattern. The entries show no sign of the next major capability, so its timing is unclear.
Slack
6.3COMMSCOLLAB
Slack now hosts any A2A agent without Slack-specific code.
◆ Current state
Slack's developer channel is almost all agent plumbing. On 10 November Slack became an A2A (Agent2Agent) client: a team hosts its own agent, publishes an Agent Card, and Slack calls it when people talk to it, with no request URL, event handling or Slack-specific logic. This follows Slackbot skills managed through Web API methods, a Slack CLI that points coding agents to the Slack MCP server, and a new requirement that Work Objects embeds allow the slack-mcps.com frame ancestor.
◆ Where it's heading
Slack is lowering the cost of putting outside agents in front of its users: first skills as code, then MCP pointers for coding agents, now a standard protocol in place of the Slack app model for agents. The platform is positioning itself as the place where agents built anywhere meet the people who use them.
◆ Prediction
Expect more A2A follow-ups, such as agents appearing in Slackbot or skills surfaces and richer Agent Card features, given how fast the agent releases have stacked up since October.
Alternatives to Stalwart 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 Stalwart or Slack.
Twilio
Twilio's voice AI stops cutting callers off mid-sentence, using its own turn-taking model.
Salesmsg
Salesmsg adds call-back requests and a one-click Emergency Stop for all outbound texts.
Element
Element 1.12.35 follows the call picture-in-picture release with one desktop storage fix.
Krisp
Krisp moves call transcripts and live captions to cloud transcription in KrispCX 2.84.4.
Misskey
Misskey 2026.11 ships: a leaner start script, and Node.js 22 no longer boots.
See all Stalwart alternatives → · See all Slack alternatives →
Recent activity from Stalwart and Slack
Latest ship moves from both products, interleaved chronologically. ⚡ = editorial spark.
- 4d agoSlackBring your A2A agents to Slack ⚡
- 8d agoSlackWork Objects embeds require the slack-mcps.com frame ancestor
- 10d agoSlackSlack CLI 4.13 tells coding agents about Slack MCP and Skills
- 10d agoSlackSlack Skills Plugin installs in Claude Code from its own marketplace
- 12d agoSlackUpdated low-usage submission criteria for Slack Marketplace apps
- 15d agoSlackSlack CLI 4.12.0, the fourth CLI release in October
- 26d agoStalwartv0.16.27: IMAP SEARCH RETURN and iTIP time zone fixes
- 1mo agoStalwartv0.16.26 fixes RocksDB rewriting every blob on compaction
- 1mo agoStalwartv0.16.25: JMAP MaskedEmail and Autodiscover fixes
- 1mo agoStalwartv0.16.24: PowerDNS provider and phishing list matching fix
- 1mo agoStalwartv0.16.23: nested list delivery and lost DSN fixes
- 2mo agoStalwartv0.16.22: STARTTLS session reset and DMARC result fixes
Frequently asked questions
What is the difference between Stalwart 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 Stalwart 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 Stalwart?
Top Stalwart alternatives in Comms are ranked by recent ship velocity. Browse the "Stalwart alternatives" section above for the current picks, or visit /alternatives/stalwart 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.